Just checking because of the circular mark - do u have plecos in the tank?
1. Please explain the problems with your fish. When did you notice the problems and did anything unusual happen that you think started them?
On Tuesday, 1/30, I came home from work to find my pair dark of color and hiding behind the sponge filter. The heater was hanging off of the suction cups, and my female had a white semi circle on her side. Tested the water to find a 1ppm ammonia spike. The tank was properly cycled, and the fish have been in there for several weeks, so it wasn't a crash. Did 80% water change and they returned to their color.
The next morning Wednesday 1/31, they were acting strange. .5 ppm but there was no waste or food in the tank. Did a good dose of prime, since I didn't have time to do anything (had to go to work). Came home to 0ppm. Did a 50% water change, as Wednesday was a normal water change day. They were fine and eating happily.
Thursday, 2/1, the female was hiding behind the sponge and behaving very erratically. Glass surfacing, flying around the tank into objects (glass walls, sponge, heater), and has very dark stress bars. The male is behaving and looks normal.
2/2, today, is the same problem as yesterday.
2. Symptoms (i.e. turning dark, excess slime, not eating, clamped fins, flashing, darting, clamped gills, white/yellow/green poop, hiding, headstanding or tailstanding, white on tips of fins, rotting or fungus, blisters/white zits on fish, bloated, cloudy eyes, wounds).
White semi circle mark (presuming from heater burn), dark color, darting
3. What medications/ treatments have you already tried and what were the results. Include dosage and duration of treatment.
Water changes, no meds. Not sure what to treat with anyways.
Tank/Water
4. Tank size and ages, numbers and sizes of fish.
A pair in a 20 gallon. Around 6", around 2 years old.
5. Water change regime (What percentage and how often).
50-70% 2x a week
6. How long has tank been running? Is it bare bottom? If you have substrate, what type and how deep is it?
Bare bottom, properly cycled, running for several weeks.
7. Do you age your water? If you do for how long and what is the ph swing.
Unable to age water, since I have no room to put a container or barrel.
8. Parameters and water source;
Tap water.
7.2 ph
0 ammonia
0 nitrites
5-10 nitrates
~115 tds.
Tank water reflects that.
Just checking because of the circular mark - do u have plecos in the tank?
Is your sponge the crappy type with fine pores that clog every couple days?
Is a 20H fine for that water change regiment? Sounds like they respond well to new water.