The most important parameters are three that are generally included in what is known as the nitrogen cycle, all of these compounds contain nitrogen.

1. Ammonia/Ammonium (NH3+/NH4+): 0ppm
2. Nitrites (NO2-): 0ppm
3. Nitrates (NO3-): ideally as low as possible.

These all can ideally be tested for with a liquid test kit, ensure when buying it is within the expiry date and ideally used within a year of opening.

Ammonia is the most common liquid product of fishes waste production. It is processed via microbes from nitrites and then to nitrates in a well oxygenated environment with plenty of flow e.g. a filter.

The first two, Ammonia and nitrites are extremely toxic to fishes, hence required parameters are 0ppm. Thankfully a cycled filter provides these microbes mentioned earlier to process ammonia to nitrites.

Nitrates are removed by water changes and slight amounts are removed by a large amount of plants. This is less toxic but long term exposure is best avoided.

Going further on and a little more complicated are parameters you might encounter. Their importance varies and I have still yet to have an entire understanding on their effect on fish health.

pH: This doesn’t entirely need a definition other then a measure in a logarithmic scale (each value is 10x larger then the next).

TDS: Total Dissolved Solids, all the dissolved solids within the water. It is a bit vague but many of these can be vital for fish and plant health.

Conductivity: Actually very closely related to TDS but, it’s a measure of charged ions.

GH: General hardness, measure of certain metals.

KH: Carbonate hardness, now this is the difficult one as it is often confused and used interchangeably with carbonate alkalinity. Going beyond basics there. This makes it a little bit more complex as a measure.

All of these measures/parameters are interlinked and related. So, these last measures are really species specific, they depend on the fish you keep and where they originate. The adaptability of fishes to any of these has not been discussed entirely in the hobby. To put it simply though fishes do require some aspect of these for bone health, the extent needs discussing further.