There are several elements to water chemistry that we need to keep in balance in order to ensure the aquarium is healthy. This guide will help you make sure this occurs as passively as possible (i.e. the aquarium is self sustaining) but it will be necessary to at least monitor and in most cases do a bit of work in even the most balanced and self sustaining aquariums. 

Water changes should be conducted every few weeks depending on the type of aquarium.  Read here for information on how to do conduct a water change and the ideal frequency

Remove dead organisms immediately.  Leaving dead fish, invertebrates, or coral can lead to a rapid decline in water quality. If possible, move questionable corals, plants, and even rocks to a separate system. This could even be a 30 gallon bin which you fill with water from the aquarium from which you are pulling water out of for water changes. This will remove the source of potential contributors to the water fouling. If you think that a coral is dying, it almost certainly is. You can pull it out and smell it. If it is putrid, get rid of it.

Check the thermometer. This is so obvious that it can be easy to overlook. A problem with the heater can be catastrophic. The correct temperature should be 74-82 degrees Fahrenheit. Ideal is 76-78 degrees Fahrenheit.

Check the pH. You want the pH to be around a 8.1-8.4.  Follow this link to pH description

  • It is much more common for the pH in a neglected or acutely crashing tank to be low
  • This can usually be fixed by solving the underlying problem and then doing multiple 25% water changes. It is important to replace the water at 10% volume of tank per hour or less. For example, if you have a 55 gallon aquarium, take out 15 gallons initially and replace 5 gallons per hour.
  • If your pH is too high, it is likely that the water you are using for water changes is very hard (usually well water) or you over dosed a buffering product
  • Using buffering products in anything but a very successful reef that is drawing carbonate for growth is a temporary fix and usually a band-aid to an underlying problem. It's like using an air freshener to cover up the smell the dog feces sitting in the middle of your living room

Test nitrate and phosphate levels. These are the two indicators of how much waste is being produced and not reincorporated into your system. When they are both low (nitrate under 10 ppm, phosphate under .5 ppm) and there are no other abnormalities, generally a water change is not necessary.