Hard telling what's wrong, But I'd start with a couple of water changes this week. 30ppm is high considering you do water changes and youhave live plants. I also think the temp is higher than it need to be. Try to keep him in the 70-75 degree range. I'd also quit feeding the blood worms. You need to get him something that is nutritionally balanced. A pelleted food like Retpilemin is the way to go for a basic diet. Since you have no discus it might not be a bad idea to get rid of that buffer also. The biggest problem with those products is water stability. Just use your tap water-declorinated. That way it is always the same ph. The buffer product is probably the culprit causing the high nitrates also.
As far as looseing his color, that is a good thing and it is normal. Do some searching around this board. There are a couple of threads about the dyed frogs.