My current problem is with one glo danio, but I've had ongoing issues (different ones) with many fish. I have no idea what's wrong with the danio, so that's my immediate concern, but also just want to figure out if I have an overall problem.
I'll try to answer all the questions in the sticky:
1~What type of fish is afflicted? In addition, please describe what is wrong with the fish to the best of your ability (i.e. cotton like growth, bloated, etc.).
Glo danio is looking terrible. No cotton-like growth, but he looks all misshapen from his... jaw?... to his middle, and a small piece of his tail is missing. And he's skinny. I'll attach a pic.
2~What are your tank parameters (ammonia, nitrites, nitrates, temp, pH)? Please give exact values.
Ammonia: 0, nitrites: 0, nitrates: 20, temp 75, pH 7.2. These numbers have been COMPLETELY consistent, every time, since the tank was cycled in June 2017.
3~ How large is the tank? How long has the tank been set up?
20 gallons since June 2017 (9 months)
4~What type of filtration are you using? Please give the name and number (i.e. Fluval 304) and amount of gph
Marina Slim S20
5~How many fish are in the tank? What kinds of fish are they and what are their current sizes?
4 platys (3 adult, one juvenile)
6 glo danios (adult) and one 6-week-old fry
6~When is the last time you did a water change and vacuum the gravel? How often do you do this? How much water do you remove at a time?
Today. I do a 25% change every week and I vacuum the gravel.
7~How long have you had the fish? If the fish is new, how did you acclimate it/them?
Had this fish for about 6 months.
8~Have you added anything new to the tank--decor, new dechlorinator, new substrate, etc.?
9~What kind of food have you been feeding your fish, have you changed their diet recently?
Same as always: Spirulina 20 and very rarely freeze-dried brine shrimp
Here's the overall story:
I got the three platys first and cycled the tank with them in June 2017. They're all doing great. The only issue I had (recently) was that one platy had two flat white spots (not raised, not ich) on her tail, but that went away on its own.
Then I added three guppies in July 2017. The male died very quickly (within a week or so). One of the females is still alive, the other one died completely out of the blue maybe a month ago. She looked fine until I found her dead.
Then I added 5 danios from one pet shop around August 2017. Although I thought they looked fine when I bought them, over time I noticed some of them seeming to get skinnier/less "rounded" even though they were eating plenty and swimming around just fine. I added three danios from a different pet shop at some point. All three of the other pet shop's danios look completely different from the original ones... they're clearly much healthier, bigger, fatter, etc.
Finally, I added a honey gourami.
The honey gourami developed dropsy after about a month or two and died quickly. One of the original danios died unexpectedly the next day, no signs of dropsy.
So basically, I feel like I've had a few different problems and yet all the parameters look perfect every time and I'm trying really hard to get things right.
The only other problem I've had is that the diatoms will NOT go away. They started around October and persist six months later. I have taken decorations out and scrubbed them (just with my hands and water) and within 2 weeks they're brown again.
I have the lights on a timer currently on for 10 hours a day because more light is supposed to be good for diatoms. I also used PhosGuard for about a month to try to get rid of diatoms, but it did nothing.
The only other thing I can think of that could be a problem is that it's rarely completely dark in the room with the fish. It's my office and I work overnight hours, so even though their light is off, there's ambient room light for all but about 3 hours a night.
Limitations: I don't have a quarantine tank. My current heater is pre-set to 75 and can't be changed. I'd ideally like to get a quarantine tank, but I don't want to go through the expense of it if I can't get this tank stable, because this has become a really frustrating hobby!
I welcome any advice. Sorry this was so long.