African cichlid who wont open his mouth

Question
Hi, I have an African cichlid (only one) who, when i returned from work the other day had a swollen disfigured mouth and big puffy lips. I cleaned the gravel, replaced 30% of the water at least but did a few more subtle changes over the last 2 days, replaced part of the filter and administered something with formaldehyde and malachite green. His colour is back, he is happily swimming around, but it's like he doesn't even notice when I feed him, he doesn't eat, sometimes he will swim up to food and just bump into it. Usually he is quite aggressive about eating and I am quite worried. I have added pellets that are supposed to have vitamins for healing to his normal flakes. The pH was a bit high but i fixed that as soon as I noticed and I check it quite regularly. It seems that he can't open his mouth perhaps? As for holding eggs, his fins come to a point, he has a spot on his back fin, I'm quite sure it's a boy.

Answer
Hi Sophie,
African Cichlids live in a high PH.  8.0 -8.5 depending on which one you have.  Bringing down the PH with chemicals is not recommended as it tends to make the PH fluctuate, which can be deadly to fish.  When the PH is too high, and we bring it down too fast, this is very dangerous for fish, and so is bringing it up to quickly.  Have you checked your ammonia, nitrites, and nitrate levels.  Ammonia, and Nitrites must be zero, and nitrates should be low.  The smallest amount of ammonia or nitrites is deadly to fish.  Check these first to see if your water chemistry is right.  To bring down your PH add driftwood to your tank, and you could also filter through peat.   It is always better not to use chemicals as these could harm your fish.
He is not feeling well, as sick fish refuse to eat.  Test your water, and write back to me telling me as much details has you can on your fish.  Tell me what he eats, his cichlid name, the size of his tank, and the temperature of his water.  Are his fins clamped. or  ragged, or are them normal?  Is his mouth back to normal?  I must know these things.  The more you can tell me the better I can help you.
Lynda