Ahli

Question
I had an 8 inch ice blue ahli and i had it for 1 year in a 55 gal wth a magnum 350 full of carbon and zeolite with a fluval 404 with ceramic cubes,bio balls,carbon and ion exchange resin he died and i cant understand why he would die? my water has lage amounts of coral in it so it stays at 8.0 there is only 3 other fish in it 2 lage jack dempsys that have lived in high ph all there lives and they arnt compatable so they keep to them selvs by trying to mate and a pleco ive never had a fish die in my tank before and he was the best fish i had.my akilinity is high and it satys high b/c of malawi salts i fighured the j/d would die before him im really the jack dempseys had nothing to do with it!i watched for hours and they never harassed him it was always the other way around they kept in there corner and he swam all aroud and was very agressive. i checked on him before i want to bed he was fine and feisty and i woke up and he was dead.i carry out water chanes one per month and gravel cleaning once a week,

Answer
Hello H,
I agree that Ahli Cichlids are really pretty. I'm not one hundred percent sure why yours might have died. You have really good filtration at any rate. Had you checked the ammonia/nitrates level recently before he died? If so, and they were either low of taken care of by water changes, then the only other explanations I have for you is that either he died of old age (was he full grown when you got him?) - since most Cichlids live usually no more than 5-7 years in an aquarium, or your Dempsey's did in fact attack him. Ahli's are usually recommended to have a larger tank, and I have heard from some that there should be around 4 females to prevent "spawning stress."
The coral you may want to remove, especially if any parts of it are sharp. You can instead add ground up bits of certain shells that will add alkalinity to your tank.  
Lastly, whenever you gravel clean, you may want to re-seed your beneficial bacteria, because a lot of it will be living in your gravel. Sorry about your fish, and hope you have better luck next time.