Please Help! sick Flowerhorn fish

Question
Hello Chris,
Tank has been set up for 2 years. 50 gallon. Flowerhorn, 1 very aggressive fish can't keep anything in the tank except gavels. Marineland Hot Magnum filter (the type that hangs off the side of the tank). not sure pH, we put freshwater aquarium salt and stress coat solution every time we change water. Water change about every 4 months (we were advised not to change often by pet store). we usually dump out 1/2 tank and vacuum out the sediments. My fish is always active, he gets into his attack mode whenever someone is near the tank, anything we throw in the tank he will attack and eat (ghost shrimps, gold fishes, crawdads, ect.) He's always been healthy w/ good appetite, he's about 14" across, and 5" thick. Last night when we got home from from work he is laying flat on one side and not moving at all. This has never happen before, not even when he is sleeping. We used a small net to test his reaction, usually we don't dare to stick our hand in the water because he bites. But he shows no movement, he's gill is moving like he's breathing normally, but he is not swimming at all, so I picked him up with my hands to see what's wrong with him, he flinched a bit and trying to get away from me but only his left side fin moves like normal, the right side has no movement, I tried to "swim" him to see if he starts to move, but all he can do is float and sink to the bottom, we also noticed he's body is oddly curved to one side. We are very worried that we are running out of time to save him. PLEASE HELP! Thank you.

Answer
Hi Patty;

That does not sound good at all. It could be a stroke, aneurism, heart failure, etc. Poor guy. I'm afraid the very bad advice given to you by the fish store has caused him to become gravely ill. All fish, especially large ones like yours, need at least a 25% water change every week along with a gravel vacuuming.

I don't know if anything is going to help him but you could try making a partial water change of 25% every day. It will lower the dissolved wastes that have accumulated, hopefully without stressing him further. Make sure the new water is the same temperature as the old water and use a water conditioner.

Adding water for evaporation does not count as a water change. Waste does not evaporate. It has to be removed. There is undoubtedly a very high level of nitrates (NO3) in that water by now. Nitrate is the end result of the biological filtration that occurs in your tank. The water may look clean and clear, but you can't always see dissolved organic wastes. Water clarity is not an indication of water quality.

Below is a link to a good web page that tells more about their care. Your fish store apparently has NO IDEA how to properly care for your fish. Shame on those people... If I were you, I would never go back there.

http://www.flowerhorn.co.uk/flowerhorn-keeping.php

Hoping for the best and wishing I could do more...

At Your Service;
Chris Robbins