Guppies swimming at top of the tank


Hey everyone!

I keep having this issue where a guppy will stay at the top of the tank. Not in the typical, just swimming around at the top but they will have almost an arched back with their head at the very top/surface. And then they almost always die a few hours later. This has happened several times but none at the same time. I’ve lost 5 guppies in a span of about 4 days.
Ammonia is at 0, nitrites are at 0, and nitrates were near 0/negligible.
PH was low in the beginning at around 6.2, I added some API ph up and it went up to 7 over the next few days. Stayed pretty consistent at 7.0 until my last water test and it was an 8.0. Nothing in the tank has changed other than doing water changes and vacuuming the gravel.
Water temp is a constant 80°F
Tank is about a month old so not fully cycled, but I have been doing daily 25% water changes and testing water Params nearly everyday (sometimes every few days if I’m being honest)
It is a 37 gal tank, 3 gouramis, 15ish guppies, 2 kuhli loaches, and some ghost shrimp.
I have a bubbler in there and my filter agitates and splashes so I don’t think it’s a lack of oxygen otherwise all the fish would be dying at the same time right ?

any ideas or suggestions?

ps. I am aware of the nitrogen cycle (now) after I killed a bunch of fish. People at petsmart said just add this quick start and you can add fish in. Well that isn’t how any of this works lol

Update: I check the tank this morning and 3 more guppies had died. 2 of which I have notice doing the arched back, head at the surface behavior last night when I last checked on them. Not sure if the other one was doing that or started doing it after I went to bed.


Welcome to the forum. Did you recently buy these fish? I'm asking because difficulty keeping commercially raised guppies alive longer than about a month is pretty common. If that's the case here I'd suggest trying to find some raised by a hobbyist. If you have a privately owned fish store (as opposed to the chains like PetSmart), they may have locally raised fish, or you may be able to find them on Facebook Marketplace (or whatever it's called; I still don't have a Facebook account).


I'm experiencing something similar. Bought three guppies at a local fish store (not a chain), which quarantines all of their fish. Everything was good for three weeks then one morning one of the guppies was missing. No clue where it went. Best guess is it jumped out and my cat ate it. A week later one of them had a swollen belly and was hanging near the top of the tank. Two days later and he's dead. Another three days has gone by, and the third one is dead as of today. No clue what the issue is. All the other fish and shrimp in the tank are perfectly fine. The tank has been running for 2+ years and is well maintained. It's a planted tank and I'm injecting CO2, but also run a bubbler. Water temp was 73 when I introduced the guppies and I recently increased it to 76 because I learned they can have issues digesting food at cooler temps. Any ideas?

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