Crystal clear water is a very important factor in keeping the snapper, or any other turtle, happy and in good health. All of the aquatic turtles eat, sleep and relief themselves in water. They have no choice but a constant ingestion of what they live in. Filthy water causes growth of bacteria, and combined with PH and ammonia level unballances, might result in developing of fungus and shell rot to mention just the basic and common diseases.Swallowed dirty water results in digestive systems complications and development of parasites. If not treated properly, all of the above mentioned could cause serious injury to the animal or even its death.

Therefore, a proper filtration system and periodical PH and Ammonia level check ups are necessary. Turtles are quite messy and foul water much faster then fish. The filter supplied to the turtles should be much more powerful then the one used for a fish tank, and in fact a combonation of an internal and external filters should be used.
I use the Fluval filters of both types ( Fluval 3 or 4 ), and a box type external filter with 10 l/min capacity pomp. In choosing a filter I always pick the ones that will guarantee the full amount of water being filtered at least 10 times in one hour.

With periodical partial changes of water ( 2 - 3 times a week ) and always scooping out all the not eaten food and excrements ( if possible ), such a set up will allow enough time for the development of " friendly bacteria " necessary for the biological filtration. It will take about 10 to 15 days and past that time the level of ammonia in the tank will drop drastically. With unsufficient filtration the filters will get plugged very soon and having them cleaned will stop the bacterias growth.

Just like with choosing the tank, the rule would be - the bigger the better.