Interesting theories everyone. After running several tests, I have a theory of my own: I believe it's my own bloody fault for not putting up a bunch of cash for substrate. I used sand. boooooooo... here's why I think that:
I had changed out nearly all the water yesterday and switched it with the new dechlorinator, which, if it WAS the amquel plus's fault, should have reduced the ammonia to nothing. However, not two hours ago, the ammonia is somewhere between 5 and 7.5ppm. fish seem OK so I'm not going to worry about switching substrates tonight........ anyway, on to the other tests,
PH out of the tank is as low as my stupid color reader will read - 6.2 (possibly lower, but I don't FEEL anything when I stick my arm in the tank, not even itchy, I know that doesn't mean anything, and I really need a broader test... anyway...)
Out of the tap, no dechlor no nothing, I get 0 ammonia, 7.2 PH.
Out of the tap, in a clean bucket, using the amquel, I get PH 7.0, ammonia still 0.
three hours later, the results are the same from that bucket.
From a different tank, which gets the same water treatments as the angel tank, my ammonia is 0, my PH is 7.0. - this tank has a sandy bottom also, but the sand itself is of a different consistency, I should have thought that the place the hardware store gets the sand from might not be the same each time....
IN the angelfish tank, I have a fluval hooked up to an overflow filter, no carbon in the filter, and it's about half-full of healthy-looking plants and the tank walls are about half-covered in hair algae... (should have alerted me to the high ammonia... I shoulda caught it before wasting 20 bucks on fancy plecos...) I have no weird decorations, just slate and driftwood. The only thing really different between the two tanks is where and when I purchased the sand substrate... and well, the species of the inhabitants, the sizes of the tanks.... the brand of filter... ok, there's a lot of differences, but the differences that count to ME would be the sand. I've currently got some of the sand from the afflicted tank in a bucket drying out - I'm going to get some fresh water and do some tests to see how high the ammonia gets with just the sand, and also with just the sand and the water conditioner.
If I HAVE to tear my whole bloody tank down, I'll do it, but I'll only do it after I get paid on friday.
......I'll need another bucket.