Corys floating at top of tank
Came home tonight and I thought I had several dead Corys in my 20g community tank. They were floating vertically at the top of the tank but eventually moved. They were fine when I fed them this morning. I had a platy die a few days ago of unknown causes. I did a WC when I got home and dosed a little extra prime in case there was a mini-cycle (since my test kit just ran out and I can't check until tomorrow). They perked up a little and a few were swimming around but several are still kind of "floating". Any ideas what caused this? All the other inhabitants are fine, the tank has been set up and peaceful for a while now, the only change is I trimmed a bunch of plants because it was getting overgrown.
(I know everything in the form doesn't apply, but hopefully it helps).
How many gallons is your tank? 20 gal
Does it have a filter? yes, HOB & sponge
Does it have a heater? yes
What temperature is your tank? 77
Does your tank have an air stone or other type of aeration? yes
Does your Betta have tank mates? What kind? 5 peppered corys, 20(ish) RCS, 1 female betta, 2 platys
What food brand do you use? combo
Do you feed flakes or pellets? combo, betta pellets, flakes, frozen brine shrimp, algae wafers
Freeze-dried? occasional blood worms
How often do you feed your Betta? How much? brine shrimp 4 days, pellets 2, fasting 1 day, algae wafers to supplement
Before your Betta became ill how often did you perform a water change? Once a week
What percentage of water did you change? 30%
Do you vacuum the substrate or just dip out water? Vacuum
What additives do you use? Prime, ferts
What are your water parameters? Please give exact numbers. If tested by pet store please get exact numbers. "Fine" or "Safe" won't help us help you.
Just used up the last of my test kit, but tank has been cycled and stable for while, last readings a two days ago were normal
Symptoms and Treatment:
When did you first notice the symptoms? This evening
How has your Betta’s appearance changed? Floating at top of tank, thought they were dead
How has your Betta’s behavior changed? Fine this morning
Is your Betta still eating?
Have you started treating your Betta? If so, how? Water change, add prime in case of mini-cycle
Does your Betta have any history of being ill? No
How long have you owned your Betta? Was he or she ill or suffering some sort of damage when purchased? Corys have been in tank for over a month