Water Parameters

My thanks to Leveckio, who kindly made some very useful suggestions to make this better.

Water Chemistry

It’s something most fish keepers should try to understand, but many of them do not. New keepers often aren’t aware that water parameters even exist. It can be a bit difficult to wrap your brain around some aspects of aquarium water chemistry at first, but patience and persistence in learning about it all will pay off.

It took me a disturbingly long time to get a grip on the basics of water chemistry and I still have plenty to learn about it all.

When we are asked what the parameters are in a fish tank, most often what comes to mind are levels for ammonia, nitrite, nitrate, pH and perhaps temperature. But there are other important parameters in our water that can have dramatic effects on the livestock we keep.

Let’s begin with hardness. Water is frequently described as being either hard or soft. Just how hard the water is that you get from your tap depends on the amounts of hard water minerals in the water. These minerals are calcium and magnesium but they’re not the only minerals or metals you find in the water, they’re just the ones that make water hard.

If you’ve ever seen scale buildup in a kettle or a coffee maker, you have seen hard water minerals - they are a large part of what makes up that scale. The harder the water is, the more calcium and magnesium it contains. Hard water will leave whitish spots where any droplets dry out on surfaces.

Soft water has much lower levels of these minerals in it. Many people find that soft water feels rather slippery on the skin compared to hard water and detergents and soaps will lather and clean much better in soft water.

It is more difficult to rinse out all the soap in soft water than it is in hard water. Hard water has a tendency to make your skin feel squeaky clean when you rinse off the soap, but it may also make skin feel drier. Soft water usually won’t make your skin feel dry. This may be partly due to how genuine soap tends to react with the minerals in hard water; they form soap scum in hard water. Soap scum does not form in soft water.

Water softeners - a problem for the fish

Many homes have water softeners to soften very hard water. Water softeners remove the calcium and magnesium ions, replacing them with other ions, often from sodium. Water softener softened water is not suitable for fish keeping unless you add back into the water what the softener removed and even then, only provided that the proposed fish won’t mind the added sodium. Though it’s not a huge amount of sodium, it can pose a problem for many fish species.

Usually at least one tap in a home will be left off the softener system and typically there will be a bypass of some kind that you can access to get water inside the house that hasn’t yet gone through the softener, though it may not be convenient to get water that way for fish tanks. The tap that is most often left off the softener system is the outdoor or garage tap, and that can pose a problem if your area has cold winters.

Other homes may have an RO filter installed. RO is short for Reverse Osmosis. It’s a filtration system that removes everything from the water including ALL the minerals, metals, etc. RO water usually measures with a slightly acidic pH and there are NO fish you can keep in pure RO water.

Typically an outside or garage tap won’t be on the RO system either, it’s too expensive to use RO water that way. RO systems waste a huge amount of water as part of their processing. The wasted water goes straight down the drain and can’t be recovered or salvaged. The average, less costly RO filter will waste 4 gallons of water for every usable gallon you draw out of the system and even the highest efficiency RO filter still wastes one gallon per usable gallon of RO water.

RO ( along with Distilled or Deionized water) must have some minerals mixed back into it to make it suitable for fish keeping. What quantities you need to add will depend somewhat upon the fish you want to keep.

To add back in or raise the KH and/or pH, you usually would use sodium bicarbonate ( pure baking soda) and that is baking soda, not Baking POWDER, which is a very different thing.

To add back or raise the GH, you’d use pure magnesium sulfate ( Epsom salt ) and calcium chloride. There are many commercial products made for this purpose also.

Plain, unadulterated Epsom salt is very easy to find. Any pharmacy will have it and the larger the jar you get, the cheaper it will be. Calcium chloride isn’t hard to find either these days. It is sold for cheesemaking, to deice the driveway and is also used by those who keep reef or saltwater tanks. So, most stores that sell supplies for the saltwater keeper will sell calcium chloride and you can often also find it where DIY ingredients are sold to make fertilizers for planted tanks or hydroponic growing.

RO & distilled, or DI ( deionized) water, which is most often created by means of steam distillation, have a GH and KH of zero and often a very slightly acidic pH, though it should be pH 7. Both are unsuitable for fish keeping without being remineralized.

However, both RO and DI water are absolutely suitable for topping up a tank to make up for evaporation, because using them that way, they will not alter any of the parameters already existing in the tank.

About PH

PH tells us how acid or basic a substance is. It’s a measurement of the concentration of hydrogen ions in the substance. The scale goes from 1 to 14, with 7 being considered neutral. A reading below 7 is termed acidic and over 7 is termed basic. Basic is also often referred to as alkaline but that can sometimes be confusing, so it’s better to refer to it as basic.

GH, KH, and pH all have their own impacts on fish health but it’s not usually necessary or even a good idea to try to alter your tap water to match an arbitrary set of parameters you read about for some particular fish species unless perhaps you wish to breed a difficult species.

The stability of the parameters in a tank is what is most important to fish and particularly so for pH. Stability will always be more important than meeting some particular pH value will be.

Other effects of pH on our tank water

Fish keepers should also know that pH affects both the physical form and the level of toxicity of both ammonia and nitrite in water.

Ammonia that we need to worry about is the ‘free’ ammonia ( NH3). This form becomes more and more toxic as the pH rises. There are some charts showing these ratios that you can find online that will show how much NH4 to NH3 there is in water at varying pH and temperatures.

But ammonia won’t be a huge problem issue until your water hits roughly pH 7.2. That’s about where NH4 begins to convert to NH3 and the higher the temperature and the higher the pH, the more toxic the NH3 becomes to the fish.

Conversely, NH3 converts to NH4 ( ammonium ) as the pH falls below 7.2. Ammonium is not toxic to fish and not a big worry.

Fish actually respire ammonium but that usually converts almost instantly to ammonia in average pH levels. Just how much ammonia there is will be related not only to the pH of the water surrounding the fish but also to the temperature of that water.

With nitrite, the effect of pH works in reverse. Nitrite, NO2, becomes even more toxic as pH falls as it will convert to nitrous acid, NHO2. At a basic pH it remains as NO2 and while it’s very dangerous, it’s a bit less dangerous than NHO2. So there’s always a tradeoff of some kind.

Leveckio kindly explained to me that this conversion of ammonium to ammonia is due to a process called protonation. Temperature has an effect on protonation, with higher temperatures resulting in higher toxic ammonia levels, where lower temperatures result in more ammonium instead.

The pH level will also affect how efficiently the nitrifiers ( BB or beneficial bacteria) in our filters can function. At pH 8.3, the nitrifiers we rely on for ammonia and nitrite conversion are 100% efficient. At pH 7, that falls to about 50%, and by the time the pH drops to 6, the nitrifiers will start to go dormant. By pH 5.5, they’re all dormant and no longer converting any ammonia, but, at pH 5.5, there isn’t any NH3 to speak of to convert anyway. The bacteria won’t die, they’re just not working anymore and given a higher pH, they’ll recover quite quickly.

So in a high pH environment, nitrifying bacterial colonies need be only half as large as they’d need to be at pH 7. Not that we can really tell how big the colonies are, but I find it rather interesting just how much pH can affect their productivity.

Testing pH of water isn’t terribly difficult but unless you use a digital pH measuring device, it always means matching the colour on the test to a colour patch on a printed chart.

There are more than a few people who have varying problems matching the colour of the test vial or test pad to the colours on the accompanying chart and interestingly enough, men have more trouble with this kind of colour matching than women do. There is plenty of research to back that up, btw, I’m not picking on all you guys here, it’s just one of those gender differences we’re stuck with.

For any test where you must compare colours, try to read them in daylight, it’s the best light source to get the best colour rendering for this purpose. Under a daylight type light bulb, be it LED or flourescent, is also pretty good. Try to always read your test results in the same light every time.

If it’s tough to match the colours you can try placing a vial right on a colour patch and then look down through the vial. If you can’t see the patch, that’s a match. If you can see it clearly, not a match. Be prepared that you won’t always get a very close match, so you have to do the best you can and let’s hope you are not suffering from any of the many forms of colour blindness.

Many standard pH tests don’t read higher than pH 7.6 or so. If you have very basic water, you may need a High Range pH test. If your water’s pH reading is naturally higher than a standard test can read, the High Range test will be essential. If your water comes from a limestone aquifer, it could be over pH 9.5.

Extremely acidic water samples may also not register on a standard pH test, which may only go to pH 6. In that case, a Wide Range test may be needed. If you suspect that the water may be very low in pH, or if your standard pH test turns instantly to the yellow of the lowest possible reading, then a Wide Range test will be best.

Bear in mind that the pH scale is logarithmic. This means each full point on it is 10x higher or lower than the one immediately above or below it.

So, pH 6 is 10x lower than pH 7 & 100x lower than pH 8. A pH of 3 is 10x lower than a pH of 4, and 100x lower than a pH of 5. So while it might appear as if there is not very much difference between 7 pH and 8 pH, there is a significant difference. The difference between the intermediate points on the pH scale, such as 7.5 and 7.6 or 5.4 and 5.3 isn’t as daunting.

You should also leave any water sample you wish to test for pH out overnight at least, to get the most accurate reading possible. Ideally, run an airstone in the sample or shake it up periodically.

This allows any trapped carbon dioxide to gas out of the sample. CO2 gets trapped in the pipes, and it is very acidic, so trapped CO2 will cause pH to read lower than it truly is. Planted tank enthusiasts who add CO2 to their tanks are well aware of its acidifying effect. After your water sample has been sitting out for 24 hours, or more, you’ll get a much more accurate pH reading.

What is GH & KH?

GH is a measurement of the hard minerals in water; magnesium and calcium. GH means General Hardness. The measurements are usually expressed in one of two ways; ppm/ PPM, (parts per million) or in German degrees, which can be written as DGH or dGH, with a number before the letters, for example, 10dGH means 10 degrees of German Hardness. There are several other hardness measurement systems out there you may find and there are a number of sites with conversions online if you look for them. Liquid test kits often use German degrees while dip strip tests more often read in parts per million.

If you have lots of scale building up in the kettle or the coffee maker, you have water that has at least a moderately high GH level, if not high GH. The GH test I’ve used from API goes to 12dGH but water can have a much higher hardness reading. If your water comes from a limestone aquifer, it is liable to have a sky-high GH reading. Some of us aquarists call water like this liquid rock :-).

KH is a measurement of the buffering capacity of water. It means Carbonate Hardness. (The K comes from the German language). Also measured in PPM or German degrees, which can be written as dKH, DKH, also with a number before the letters, for example, 6dKH. Low KH can mean swinging pH, moderate to high KH means you’ll have a stable pH.

KH can be a bit more difficult to understand. You will also see KH referred to as Alkalinity. While Alkalinity also addresses acid buffering in water, the term is used primarily when referring to ocean water or saltwater tanks.

KH and pH have a closely linked interrelationship and it is not possible to change one of them without also changing the other. Because the word alkalinity refers to buffering capacity too I always prefer to use the word basic when I’m talking about pH, rather than the word ‘alkaline’.

The carbonates referred to by the term ‘Carbonate hardness’ are the buffers but in fresh water, buffers are mainly made up of bicarbonates. There are some carbonates involved in freshwater buffering but carbonates are the primary buffering agents in saltwater.

If you add sodium bicarbonate, (baking soda) to fresh water, it will raise KH and pH. Incidentally, you should never, ever, experiment with additives like this in your tank if you have any livestock in the tank. Experiment in a bucket, until you are certain of the effect you will get and only add such things to the tank after they are dissolved into some water, not dry.

GH and KH can have a dramatic effect on fish health, for a couple of reasons. Fish use the hard water minerals to control their internal fluid balance (osmoregulation )since they maintain this balance using osmosis. If GH is too low, fish may die, thanks to being unable to osmoregulate properly and if it’s much too high, the same thing can happen.

If you have no idea what these parameters are in your water, you may think your fish are sick with some disease, when in fact it is your water, all by itself, that is causing them problems.

While it’s possible for KH to be too high, it’s usually more of a problem when it’s too low. Very high KH may be a problem for some fish, though this might be because it contributes to TDS, Total Dissolved Solids, which isn’t something I’ll address here. Suffice it to say, moderation is usually best.

When KH is too low, you tend to have unstable pH and that’s dangerous to fish. Some fish and invertebrate species will do better when KH is quite low, but the majority appear to do best when it’s at least moderate. Do your research on the specific needs of the species you want to keep and test your water to find out what it has to offer.

How does KH work exactly?

Very simply, KH, or the buffers, neutralize acids. Buffers can be present in the water at any level from zero, low, moderate to high.

If something with an acid pH enters the water and is neutralized, then we can say the water buffered that acid. I might be dating myself here, but there used to beadvertisements for a pain reliever called Bufferin. It was aspirin, but aspirin is very acidic and may upset your stomach.

Bufferin had something basic added to it. It was probably calcium carbonate, though I’m not certain what it was. The idea was that the aspirin wouldn’t bother your stomach so much if was buffered in this way. Bufferin’s name referred to the fact that the basic ( alkaline) additive ‘buffered’ the acidic aspirin.

Whenever something acidic enters the water it will affect the KH level.

For example; if you were to add a given amount of citric acid to water, you might expect to see the pH reading drop lower, because acid should lower the pH. (Citric acid is widely available for use in foods and is one of several acids you could use to adjust pH in a fish tank.)

If water has NO buffers, we say it has no buffering capacity. So if you added your citric acid to water with no buffering capacity, your expectation would be met. The pH would drop and stay down.

But what if the water has some buffers in it?

We might describe water like this as having ‘low’ buffering capacity. When you add the citric acid, the pH would still drop, but it’ll drop less than it did in the water that had no buffering capacity at all.

When water contains a lot of buffers, we say it has high buffering capacity. Depending just how high the buffering capacity is, if you added that same citric acid, then you might see the pH drop only slightly or it might drop as you expect, but then bounce right back up again.

That happens because the acid was neutralized by the buffers. In actual practice, most often the pH will drop and then quickly bounce back up to its former level. How quickly you measure after the addition could make a difference to the result you get too.

But the water has changed, just because you added an acid, even if the pH did not drop as much as you expected. That’s because the total amount of buffers in that water will have been reduced. The buffers will have been used up as they neutralized the acid. If you check the water sample’s KH again, after the acid has been added, you’ll see that the KH reading is lower.

So KH is a measurement of the amount of buffering capacity your water has. There is always a limit to how much acid can be neutralized by any given sample of water before the buffers will become depleted. How long it takes to wipe out the buffers completely also depends on how much acid there is and on the pH of the acid being added.

Where does this acid come from in our tanks?

I’m sure you wonder where any acid might be coming from in a fish tank because of course, you are not adding any, as a general rule. There are some things most of us expect will make our water a bit more acidic, primarily leaves and driftwood, or peat moss. Just how much effect these things have on your pH depends on the buffering capacity of your water and how much of this kind of thing you add.

Wood and leaves don’t usually make hard water appreciably softer in a short time, because they can’t remove the hard water minerals. But they do add tannic and humic acids, which will use up the buffers and thus make the water more acidic. Given some time, some of the hard water minerals will be metabolized by bacteria and fish, so the water will get softer that way, but it’s not a very quick change, not as you’d get with other methods.

If you add lots of new wood, leaves or peat moss you’ll get more of a change but it’s impossible to be sure of just how much change you’ll see. This kind of thing is best used when you only want minor changes. If you want a predictable result every time, there are better ways to achieve that. But there are many other benefits of tannic and humic acids that only come from using the organic materials themselves.

In fact, there is plenty of acid going into our tanks every single day, from the wastes that are produced by fish and other livestock and especially by bacteria. The nitrifiers in the filter & the heterotrophs in the biofilm layer that coats every surface in a tank, these millions and millions of bacteria produce acid waste - just like bacteria in the human mouth produce acids that erode our tooth enamel.

These acids will be neutralized, as much as is possible, by whatever buffers are in the water, until such time as the buffers get used up. Ideally, before that happens, the buffers will be replenished by a partial water change, hopefully about 50% of the tank volume for most tanks, every week.

So, water with low KH can’t neutralize very much acid. This means that pH can drop, sometimes suddenly & drastically. A dramatic swing in pH or GH parameters will shock fish at best and at worst it will kill them.

If a sudden pH change exceeds 1 whole point, say from pH 7 to pH 6, in 24 hours or less, that’s enough to kill some fish. It can pay big dividends to check the water that your new fish have come in before you acclimate them to their new home. I test fish bag water for every possible parameter before I move fish into their new homes.

Do some research on your water conditioner product too. At least one of them, that I know of, can react with water that has low KH to result in a significant pH drop, which will drive you nuts while you try to figure out how water with a nice basic pH has become acidic, seemingly instantly. It is one of the Amquel conditioners that reacts this way, but I don’t recall which one. The information is on their website.

How do I lower the pH, GH or KH?

If you need your water to be softer, or lower in pH, or KH, then your best course will be to use RO or DI water and remineralize it to precisely the desired parameters.

It may be also possible to mix some tap water with RO or DI in some specific ratio to get the desired parameters.

Both of these methods are very commonly used. Many saltwater keepers mix their salt into RO or DI water rather than into tap water because that way they will get very reliable, fully predictable results every time.

Please be aware that the parameters of tap water are NOT constant! Weather and water treatment protocols can have dramatic effects on your tap water’s parameters, so it pays to check periodically, especially if there have been heavy rains, snows or drought.

Ways to raise GH, KH, or pH?

If you need water to be harder or more basic than it comes from the tap or bottle, those sorts of changes are easy to achieve.

One old and very common method was to add crushed coral or shell either to the tank or the filter.

Acidic water will dissolve calcium carbonate out of any coral or shell and the dissolved calcium will cause the GH to rise. To a lesser degree, it’ll also raise KH and pH, but more slowly, as it only adds calcium carbonate, not magnesium or bicarbonates. It isn’t a balanced way to raise GH, because fish need magnesium too, not just calcium, but it can work well for some shelled inverts who need plenty of extra calcium. But you can’t accurately predict the results of using some crushed shell, just like with wood or leaves.

You can use a commercial product made for this purpose or your own mineral salts. It’s not hard to do; quite the opposite of trying to persuade hard, buffered water to become softer and more acidic.

Water changes are KEY!

Bear in mind too, that the stable maintenance of GH, KH, and pH is one of the most critical reasons why we need to do regular, decent sized water changes. These are so important for the long-term health of our fish and even our nitrifiers. I’m a huge fan of 50% changes for most tanks every week, it’s the single best thing you can do for most fish.
Without water changes, a tank that started out very basic and hard can become extremely acidic and soft. This is known as ‘old tank syndrome’ but that’s a silly name for practicing what amounts to nothing less than lazy or slack maintenance. It can cause a host of problems for the fish and it can happen in a surprisingly short space of time if tanks are stocked to the max or overstocked. Extra and extra large water changes are even more critically important when stock levels are high.

I ran across a case where a tank that was filled with my local water, which is about 12dGH and has quite high KH (sorry, can’t remember exactly what it is just now) with a pH of 7.6, became so acidic that not even a Wide Range test could provide an accurate reading of the pH.

That means the pH in this water was less than 4.5, the lowest reading on the Wide Range test. The fish keeper was mystified as to why his newly acquired fish had died within hours of entering his tank, but he eventually admitted to the store owner that he had not done a water change for at least six months and maybe even longer. Five truly lovely, fully adult Tinfoil Barbs paid the ultimate price for his negligence.

How do I test for GH or KH?

Testing for GH and KH isn’t hard but the same issues apply as for testing pH when it comes to matching colours. API makes a liquid test that does both GH & KH in one box. Most liquid kits have you add single drops of reagent to a measured water sample until it changes colour. You keep count of the number of drops you use. When it does change colour, the number of drops you added is compared to a chart to get a reading in German degrees or PPM.

You don’t keep adding until the colour deepens, the result is taken when you first see the colour change. The chart tells you the reading, usually in German degrees. The API GH test reads up to 12dGH, but water can be so much harder than this, so you can just keep adding drops until you get the colour change and then figure out the reading.

Dip strips often have both of these tests, though the results may only be a range, rather than an exact number. But such as result might be all you need. You dip the strip according to the instructions it comes with for precisely the time it states and then you compare the colour of the pad to a printed colour chart. Dip strips can often read up to 300 ppm for GH, which is much higher than the API liquid test chart goes. Dip strips are also a lot faster.

And I’ll add one tip, learned the hard way :-). The colour chart for a dip strip test is too often printed on a paper label. It is too easy to get it wet and ruin it. I use dip strips often and I got tired of having to buy a new bottle just to get a new chart!

So I cut a chart off a new bottle and had it laminated in plastic, which made it indestructible and I can lay the strip right on the chart, making it easier to read. I usually use Tetra 6 in 1 strips which have the chart printed on two facing pages, which fold out from under the main product label. If either page gets wet, they stick together like glue, rendering the chart useless.

Just fyi: One German degree is equal to 17.9 PPM - the same for dKH.

Just for the sake of completeness, 1 mg/L is virtually equal to 1 PPM as well. The difference is negligible unless you start getting into very large quantities. If so, check one of the many online conversion calculators.

How would I significantly raise GH, KH or pH if I needed to?

It’s not that difficult. First, decide what you want to use for the purpose. You can get something like Seachem’s Replenish or Seachem’s Equilibrium (among many other brands) or you can use basic mineral salts.

If you want to use the salts, you will need pure sodium bicarbonate for pH and KH, and pure Epsom salt ( magnesium sulfate ) and calcium chloride to adjust GH.

The commercial products will tell you just how much of the product to use to raise GH or KH by some given amount, say, one German degree, so that’s not hard. Just test to be sure you got the result you were hoping for and follow the directions carefully to get good results.

If you use the mineral salts, you have to start with a little and then test after each addition. So you may have to do quite a few tests to get the desired result but it will be vastly cheaper over the long term to do it this way, especially if you are running a large or multiple tanks.

Use a good quality set of measuring spoons if you must, but it’s best to buy a scale that weighs in fractions of a gram, which is SO much more accurate. If you use the spoons, level off each spoonful with the back of a knife, don’t just scoop and dump, because that way lies an unstable result.

One method to determine the dosages

Take one carefully measured gallon of water, or make it 5 gallons or 3 gallons, whatever works for you.

The water may be RO or DI or tap, but if you start with tap water, be sure you have tested it first for pH, KH and GH, so you know where you’re starting from. Make sure the tap water has been gassed out, so it has no extra CO2 in it that might affect the pH reading later.

Decide what GH level you wish to achieve.

Then you start with 1/8 or 1/4 tsp. each of magnesium sulfate and calcium chloride, or use 1 or 2 grams of each. Add the salts to your measured water and mix thoroughly.

Test for pH, KH and GH. Write down or record your results so you won’t forget later on. You WILL forget if you don’t write it down! If you have not reached the desired level yet, add another dose of each salt and mix well, then test again.

When you reach the desired level, however much of the magnesium sulfate and calcium chloride you used to get there for your measured amount of water, just multiply that to get a dosage for the gallons in a water change.

If you intend to change your entire tank over, do it very gradually and safely. First, change 1/4 of the tank water on Day 1. Day 2, change another 1/4 of the water. Day 3, change half the water. Day 4, change half the water again. The fish will be nicely acclimated to the changed parameters after this and from then on you dose all the new water accordingly.

For KH, it’s a bit different, because you can’t change KH without also changing pH. So pH has to be the limiting factor when you are raising these values.

Decide what the maximum or desired pH should be first.

The method is exactly the same, starting with your measured amount of water and 1/8 to 1/4 tsp or 1 - 2 grams of baking soda. Test for pH and KH. Write the results down.

When you reach the desired pH, that’s where you must stop. The KH reading you get at this point should be enough to keep the pH stable, but you may have to compromise a bit because you can’t push KH higher without also pushing pH higher.

And, please, keep up with those water changes. Your fish will thank you for it.