If an aquarium is worth keeping, it’s worth keeping it well. Test kits are one of those things which help keep it well.
Yes, they make aquarium more science and less art, more depending on the readings, than on your feel of the aquarium, but really, the fish in your tank would rather live at the mercy of science than die in the glory of failed art.
Test Kits are easily available for almost all water parameters that are relevant for fish – Ammonia, Nitrites and Nitrates, pH, Water Hardness etc. Some are not so common, for example, aquarium shops don’t always have a Test Kit for checking copper (extremely toxic for snails and crustaceans) levels in water, but unless you have a specific problem in your local water supply, you can get away without being so particular about them.
Ammonia/ Nitrite/ Nitrate Test Kit
In our view, an Ammonia test Kit is an essential part of an Aquarist’s toolbox. More fish are lost to lack of attention to the nitrogen cycle than to anything else in the hobby. For more details on this, visit the section on Ammonia & Nitrites.
Test Kits are somewhat expensive, compared to the cost of the most fish. A natural question is therefore, should we skip this process and replace the fish if they die? The moral answer is of course a resounding NO. However, if the fish itself costs Rs 100 a pair, and the Ammonia Test kit itself costs Rs 1500 and the Nitrite Test kit another Rs 1000, what would you rather do? Not an easy answer here, is it?
Not recommended, but one way to overcome this is to ensure that the tank is cycled for about 4-6 weeks BEFORE you buy fish, and hope for the best. Learn more about Cycling the tank here.
If you buy fish and then start about cycling the tank, expect to see some amount of mortality. More than the sunk cost of the dead fish, its usually the frustration of not being able to take care of your fish, that will take you away from the hobby. Really avoidable.
If you really have to choose, but the Ammonia Test Kit only. Till you are able to solve the Ammonia spike, the other 2 (Nitrite and Nitrate) won’t show.
Remember the safe limit is 0 ppm. Briefly (for a couple of days), fish may tolerate 0.25 ppm as well.
pH Test Kit
pH test kits are available in mainly 2 types – color matching ones (either paper based or reagent based) and the electronic ones. Needless to say, the electronic ones are more accurate, but are also more sensitive to handling and need to be recalibrated over a period of time.
Are pH tests necessary?
If you are breeding fish, absolutely yes!
If you are keeping some of the sensitive varieties of fish, or expensive fish, you would rather err on the side of safety, then probably.
If you are keeping the commonly available and relatively cheap community fish, well, while advisable, its not strictly necessary.
Here’s the thing.
Different Fish come from different water systems, and definitely have evolved in the pH of the water locally available in their habitats. Some fish like the South American fish of the Amazon basin prefer fairly acidic water, and fish from the African lakes like more basic water, but most fish reared and sold in the aquarium trade are a product of breeding by Aquarists.
Over generations, most fish are now accustomed to neutral water pH. Even Discus and cardinal tetras, which I have now kept for years, and which have arguably very strong preference for acidic water, seem to thrive in a community tank with pH just a little south of 7. Of course, one needs to be aware of the requirement of the fish that you have, and you certainly are ill advised if you keep Discus in a pH of 8, but as long as you are broadly aware of the requirement of your fish and make arrangements to keep the water on the right side of 7 (RO water), you would broadly be ok.
pH test kits are then not strictly necessary. Even if you do test, a cheaper form of pH test kit, say the pH paper based kits are good enough for the purpose. But remember, you do need to know the pH requirement of your fish, and need to take steps to get the pH in the right direction, starting with RO water.
However, if you plan to breed fish, then pH testing is critical and exacting standards are expected. The eggs may not hatch, or the entire batch of fry may be lost if pH is not in the required range. I would strongly recommend that you get an electronic pH meter for this purpose.
Water Hardness test Kit
Normally, this is not a test you would need to perform, if you are adding RO water to the aquarium (which I strongly recommend). If you are not, then you need to assess if the water that you get from the municipal supply is hard or not, and a relatively simple and common sensical approach to this is to see the level of residue left on the surface once water has dried off from a surface like glass.
Clearly not very scientific, but a good starting point. Most fish are not very sensitive to water hardness, but harder the water, chances are higher that the pH will also be higher.
From experience of keeping fish in a community tank at home, I can say that I have rarely used a water hardness kit, and have not had any real problems so far.
Again, all of the advice above changes, if you are attempting to breed fish, water hardness measurement is of importance, but then again, you would probably be starting off with RO water (soft water), and then you would know exactly where you want to reach.
Dissolved Oxygen test Kit
Again, this is not usually a necessary test kit for the home aquarium. Not because this is not an important parameter, but because people usually have a air stone or some similar equipment, which bubbles air into the water, thus causing disturbance on the water surface and increasing oxygen levels in the water. Of course it is not necessary that this is sufficient for the tank inhabitants, and I have suffered instances of severe lack of oxygent in my community tank, even with a fully functional air pump, but the good news is that general observation of fish behavior will give you a sense when this is becoming a problem.
Fish will gasp at the surface of the water whenever dissolved oxygen in water plummets, and this should be a call to immediate action, as any prolonged instance of oxygent depletion will lead to loss of fish.
A partial water change should immediately improve oxygen levels of the tank. What should also follow is an additional source of water agitation, perhaps increase the flow of air into the tank with the existing air stone or an additional inflow of air bubble into the tank. It is also important to siphon off organic debris in the tank, as decomposing organic matter contributes heavily to depleted oxygen.
That said, a DO test is not a standard requirement of a stable aquarium set up at home. Larger water bodies, where density of fish is higher, or the fish are bigger, probably require a DO test kit, especially since its difficult to keep track whether fish are coming up and staying up at the surface for oxygen.