Hi, I've been keeping african cichlids for a while now and over the last few days, I've had an Ammonia spike which I can't bring down. I've emptied tank of all rocks to check for dead fish...none...I've stopped feeding them, no difference. I've done 50% water changes still as high day after. I've even checked the water in my tap it's 0. I've put prime in to protect the fish and started using seachem stability as though I'm cycling a new tank. I have been running this tank and fx6 filter for 6 mnths, no new fish have been added either. I'd be grateful for any ideas.