My fellow (sex uncertain), is probably about 10 inches long and under 3 years old -had him since baby). We had, what I consider, an event to which he hasn't felt like himself, since; and hasn't eaten or pooped in nearly a month that I can tell. See below.
1. Water parameters
a) Temp: 77 Deg F. (25 C)
b) pH: 7.2
c) GH.: ?
d) KH: ?
e)Ammonia, Nitrate, Nitrite, levels.: only tested for Nitrite, 0 ppm (Ammonia was fine in the past, tho)
f) Water change frequency: average 1 per week, right now 2 xs
(Most LFS's will check your water and give a list of readings).
2. Tank set up
a) Size: 30 gal
b) Substrate: small gravel, with med large rocks
c) Filtration: power filter (2 large filter system)
d) Furnishings: decorative plastic rock of 13 inch by 7 inch by 2.5 inch deep
e) Other tank mates: One angel fish
f) How long has it been set-up? approx 5 years
g) When was the last new fish added? 2007 (15 months ago)
h) Foods used and frequency?
Usually drop in 3 to 4 algae wafers every few days depending on tank algae production.
3. Symptoms / Problem description
About 1 month ago, I discovered the tank heater had been wiggled at connection and was off. I had no idea how long it had been off (one day or even a week?). Pleco had seemed a little inactive and his food (algae wafers) were wasting. I immediately plugged in the heater and let it go. That evening I checked it and it seemed too hot to the touch so I turned it down a few degrees (thinking thermostat on heater might be old). (FYI, During this period, the room temp was somewhere between 65 and 72 - autumn with the air systems off. I later let the small 10 gal tank go without heat to check its temp and it read 72 (22 C ?)) I deduced that the cooler water may have set his metabolism lower and he wasn't hungry. However, with the warmth, he took a long time to start 'moving'. The skin near his head seemed a little different in color or texture, so I dropping some stress coat over him to help protect. Seeing this, I wondered if I had overheated him. During the first week of this 'recovery' he sat along the bottom with his mouth on the filter intake tube (could not see if he was 'sucking'. As he started moving in the 2nd or 3rd week, he started almost sucking along the wall again, but it wasn't very dirty, and I saw no poop. Shortly after this period, he started lingering along the top of the water, so he could breath air, and if he dropped below, he would push up and gasp a mouthful. His stance reminded me of a whale in a vertical position, letting the flow of the filter outlets suspend him til it moved him too far and he would make his way back to that place of suspension.
I have still seen no poop nor have I seen him trying to eat the algae wafers like he used to. I am sorry I did not log the series of changes in order to be more specific. He occasionally shutters; and sometimes dashes around the tank; but usually just sits near the top. (Actually a few days ago, for a few days, he was huddling near the airstone bubbles.) His fins are finally started to show a ragged look, but I don't see problems. But he is getting very weak I think. I haven't seen him suck on anything

4. Action taken (if any)
The algae wafers continue to get old and slimy, but I only pull them out every few days. Right now, the filters are getting clogged about every week; so I am changing them. Doing about one 25% and another 33% water change every week in case I have too much organic material on the bottom - and hope that it helps (oxygen levels). I may be setting in algae wafers a little often, hoping to offer him some fresh options. Last week-end, the guy at the store thought perhaps Shrimp pellets would entice him to eat. (It hasn't).
5. Medications used (if any)
None
I have felt he was getting too big for the tank for the last year, but cannot figure out who I could trust with his life. (Now look what I have done! Gave him temp changes in two directions (the heating was surely too fast)) I was hoping he would only grow as big as the tank would support. Wasn't sure of appropriate dimensions for a happy fellow and find it hard to give a pet away. Have you any advice? Should I offer him some fresh lettuce or broccoli? Take him to a vet if I can find one? I may be too late with this query.