Water chemistry
Water chemistry is a big, probably the biggest part of an aquarium. It is what governs just about every factor within the aquarium and chooses whether your plants and fish live or die. The water chemistry will usually be what comes from your tap with a few minor adjustments, but in some cases it may need to be changed which is where it gets difficult and is often quite hard to do.

how to test water conditions aquariumpH is the most common factor people look at. pH is a measurement of the acidity or alkaline of the water, 7 is neutral, above is alkaline and below is acidic. All fish have a somewhat different preference and range. Odd as it may be, almost no fish prefer completely neutral water, this is due to imbalances in the wild. Excess of wood and mud in areas like south America will raise the pH, but drier places with clay grounds and billabongs such as Australia, support a much lower pH.


Once you find the preferred PH of your fish, you must remember that they can adapt to a wide range. Although they might be happiest at say 7.2 they would be just as happy at around 6.8 or 7.6. Cichlids are an example of a fish with a much higher pH. Limestone and coral based rocks are placed in the water to create a more alkaline environment around 8 or so. Some tetras and Australian rainbows will prefer a lower PH of around 6.5.

Changing the Ph can be hard and is not a good idea. The water contains natural buffers to restore the pH to its original value that is why liquid pH up and down will have no effect. To change the pH you must change the water buffer level. This is not recommended unless you specifically need it to breed a certain type of fish. The best way to bring the PH down is to use a commercial plant substrate, add wood to the water or peat to the filter. Peat and wood are great but may stain the water and this is impossible to get rid of.

Ammonia and Nitrites: ammonia and nitrites in the aquariumAmmonia is produced by fish waste and excretion, also excess food and decaying plant matter. This ammonia is toxic to fish and the tank must be cycled to get rid of it. A cycled tank has bacteria that consume the Ammonia and turn it into nitrites which are more toxic but luckily are instantly converted to nitrates which are relatively harmless.
If you have any levels of nitrite or ammonia it may be due to a mini-cycle caused by cleaning of the filter medium or a very large water change. It can also be due to over stocking and over feeding. Make sure you are careful to always keep levels of these down so that your fish are always safe and happy.
These will also occur when first setting up your tank, for more information visit the cycling your aquarium page.

Nitrates: Nitrates are not an immediate danger to your fish like


ammonia and nitrite but over time they will accumulate within the tanks water unless you do something about it. If the levels reach very high levels, over 25+ppm, then the fish may become stressed and not eat as much or lose their colour. It is a good idea to keep the nitrates as low as possible and there are a few ways of doing this.
The first is to have a lot of plants within the aquarium. The more you have, the more waste produced by the fish will be reused as a food for the plants. This is a great way to make a mini-ecosystem that interacts with itself and requires much less maintenance. A tank with both a school of fish and a lot of plants will require less ferts due to the fish providing the majority of fertilizer to the plants.
The second is to make sure you keep up your constant water changes, if you do this you will reduce the accumulation of nitrates in the water and sustain a healthier environment to your fish.

KH and GH: KH is carbonate hardness and refers to how much carbonate is in the water, this is not usually that relevant but if you are injecting co2 into the aquarium it is a neat way to be able to estimate how much co2 is dissolved at a point in time. Carbonate hardness will also determine how much of a pH swing you will have if you run co2 when the lights are not on, if it is higher then there will be less of a swing. You do not want your carbonate hardness to be too high but around 80ppm + is desired to act as a good buffer.
Raising your KHhow to raise your KH aquarium
A higher KH will also stop your pH slowly dropping over time, if your KH is too low it can easily be raised by using a small amount of sodium bicarbonate in the aquarium and when you carry out a water change. About ½ a teaspoon will raise the KH by about 2 degrees in 100L of water, so scale this to your tank and off you go. If this method is too temporary the other way is to use a bag of crushed coral in the filter, start with a little and work your way up, having too much may also raise the pH so take it slow.
GH: GH is the general hardness of the water. Its basically the same as when you get a drink from the tap, you can usually taste the difference between very hard water which is full of minerals and very soft water which is quite devoid.


PPM (Parts per million)


0 – 4 (dH)

0 - 70 ppm

Very soft

4 – 8 (dH)

70 - 140 ppm


8 – 12 (dH)

140 - 210 ppm


12 – 18 (dH)

210 - 320 ppm


18 – 30 (dH)

320 - 530 ppm


30+ (dH)

530 + ppm

Very Hard

Some fish prefer hard or soft water but in general it does not make too much difference. Usually as a rule of thumb, the higher the pH the higher the GH. You will find that fish prefer either acidic and soft waters or alkaline and harder water.
Changing the GH: The GH can be raised fairly easily, for a fish tank with fish requiring a higher pH,Water chemistry in the aquarium limestone rock or any rock that will leech salts into the aquarium. Coral can also be added to both the tank and filter to effectively but safely raise the GH.
To lower the GH there are two main ways. First is to dilute the aquarium water by using RO reverse osmosis water, which is cheap if you buy a RO unit. It will void the water of all its salts making it very soft and it will bring down your gH. Other ways are to use peat, wood or a softening substrate.

These are the basics for water chemistry but before you actually decide to go make any changes, realise that the fish may be just as happy as they are now and changing it will make almost no difference. It is better to leave your fish than put them through the stress of a large swing in water conditions.

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