Apistogramma Thin And Panting

Hello one and all, I have cockatoo apisto that is thin an is always gasping. Water quality is good, temp is 26 to 28 centigrade due to our heat wave.He behaves normally and the female is fine. Any clues? I do a 20% change once a week. All the others are fine as is his colour. Cheers in advance, Phill.

Just an added question - by 'good', do you mean that the water quality is 0 for ammonia and 0 for nitrite and 20 ppm (or no more than 20 ppm above your tap water reading) for nitrates? If there is any presence of ammonia or nitrite, or your nitrates are higher than this, that could very well be an explanation for whatever is causing these problems - with one (the weaker) fish usually succumbing to the effects before another. If, however, the water quality is consistently 0, 0 and <20 ppm respectively, then at least water quality can be eliminated as a factor.