Saltwater Aquarium Water Quality
Your saltwater is the ‘air’ that your fish, your plants, and other living organisms breathe in your saltwater aquarium. Having poor or unbalanced water quality is one of the fastest ways to kill your aquarium ecosystem. There are several factors that need to be carefully balanced against each other to make the optimal water for your fishies.
General Hardness
General hardness measures mainly calcium and magnesium content. Unless you’re raising sensitive fish or plan on breeding, general hardness isn’t a large factor in aquarium health.
It is important to know your water’s general hardness level and pick your aquarium residents (fish, plants, crabs, snails, etc.) that can live in your water.
| Degree (GH) | PPM | Defined |
| 0-3 | 0-50 | Soft |
| 3-6 | 50-100 | Moderately Soft |
| 6-12 | 100-200 | Slightly hard |
| 12-18 | 200-300 | Moderately hard |
| 18-25 | 300-450 | Hard |
| 25+ | 450+ | Extremely hard |
Carbonate Hardness (KH)
This measures the carbonate and bicarbonate content of your water. Carbonates act as shock absorbers and help buffer your water’s acidity and keep your pH levels stable.
Depending on your tank requirements, you probably want to keep your KH around 70 ppm.
Although there are better ways to control your KH levels, in emergency situations, adding baking soda will increase KH (and decrease acidity) while distilled water will dilute disolved carbonates and decrease KH.
If you need to make changes quickly, be cautious and start with small amounts (of baking soda or distilled water) and always have a test kit to measure the changes.
pH Levels
There’s an entire article on pH levels. But to quickly summarize, the pH measures your aquarium water’s acid level.
The scale goes from 0-14 and 7 is neutral (neither acidic or basic). 0-6 is acidic while 8-14 is basic.
If you need to change your pH level, consider your carbonate hardness level. The harder your water is in KH, the more difficult it’ll be to change because the pH will just bounce back. Conversely, the softer your water is in KH, the easier it’ll be to make changes.
Nitrogen Levels
The nitrogen levels relate to the amount of ammonia, nitrites, and nitrates in the water. The importance of these compounds is explained in the nitrogen cycle article.
The main concern here is that these nitrogen compounds are toxic to marine fish.
Phosphate Levels
The main concern of high phosphate levels is that it acts as a food source for algae and other planktons. Having high levels will result in green waters.
Normally, saltwater pH will not let phosphate dissolve in the water. However, if the pH drops, which can occur in a few days, the phosphate dissolves into your saltwater aquarium and becomes available to alge.
A pH below 8 will allow phosphates to dissolve. A pH around 8.5 will allow some phosphates to bind to walls and rocks. A pH above 9 will cause phosphates to crystallize and drop to the ground.
You want to have your phosphate level as close to zero as possible, around 0.1 ppm.
Chlorine / Chloramine Levels
Chlorine and chloramine is added to your water to disinfect it from organisms like amoebas that can cause diarrhea and other health problems.
Chlorine quickly breaks down and you can use chlorinated water just by leaving it alone for a few days.
Chloramine, however, is far more stable and will not break down. It is a combination of chlorine and ammonia, both which are highly toxic to fish. Chloramine will enter the bloodstream through the fish’s skin and block oxygen-carrying cells.
Chloramine will kill your entire aquarium tank of fish in 24 hours.