When do you think you need to change water and by how much? This is a question that has been bothering me and my fellow aquarists, novice or expert, for a long time. Here is a summary that I am offering to all fish geeks to help answering the million dollar question. The first answer is : it depends.(!!!)
For those keeping FW tanks, water changes can occur more frequently because it's easy to put your oxygenated, temperature regulated, RO water to your tank and get over with it. Many studies indicated fresh
water fishes are more sensitive to nitrate intoxication than marine fishes, esp. those are in the egg-fry stages. This being said, keeping nitrate level at 20ppm and below is a recommendation for adult FW fishes, 2ppm for breeders when you think you need to do a partial water change to reduce nitrate levels. Certain FW fishes can tolerate nitrate level >400ppm but it's not a sure bet.
What’s more interesting is most tropical marine fishes do well in relatively small home tanks (100 to 150g) with nitrate levels up to 200ppm. As I mentioned in my previous posts, I intended to test to find out what is the acute toxic concentration of the nitrate for my tank. Fortunately for my other fishes, or unfortunately for my Harlequin Tusk, I now have the data. At 300ppm nitrate my tusk stop feeding and later died due to acute nitrate intoxication. The fish was doing well in my tank for more than 5 years and during this period I had been practicing annual 2/3 water change to control nitrate to less than 250ppm for 14 years. Obvious signs of intoxication include unable to maintain swimming level and skin coloration changes (pinkish to deep blue). I was hoping I can revive him in a QT tank but it was too late. My tusk’s sacrifice is not in vain; now I know I must not allow nitrate to go above 300ppm.
For reef tank, nitrate has to be non-detectable (<1ppm), otherwise you may run into trouble.
My tusk die In the name of fish keeping science. Let salute him!!!
In God we trust; for others we need data to back our action. Do not let your nitrate level in the fish tank to go above 250ppm
Link to nitrate toxicity:
Acute and chronic toxicity of nitrate to fathead minnows (Pimephales promelas), ceriodaphnia dubia, and Daphnia magna - Scott - 2009 - Environmental Toxicology and Chemistry - Wiley Online Library