Hello, I have a 25 liter (6.6 gallon) tank setup since about 3 months, first I let the plants grow for a bit and 4 weeks ago I started with 5 guppies, only I notice stressed and odd behaviours so now I've come to a forum to see if someone can help. Actually one guppy has died already which alarmed me, now I observe them every day to get a grasp on understanding what is the matter. I bought a test kit to test for unhealthy levels, but from what's tested I can't see anything wrong, here are the levels in case anyone is wondering: Nitrate: 20-25 Nitrite: 0 GH: 6.7 deg Carbonate Hardness: 9.0 deg PH: 7.6 Chlorine: 0 Perhaps the general hardness is a bit low, I've read guppies like harder water, maybe someone can confirm that. Here I'll describe my observations. One of the fish is taking air, followed by swimming straight down, as if its trying to swallow it, the bubble either comes out from its gills or mouth, and then it repeats this for almost 2 hours after feeding. I feel like it is some kind of survival mechanism, due to she is ignoring any other fish that bite her and goes straight back to doing this process. After about 2 hours, she just gasps for air without swimming down, for about 30 minutes or so, then it just starts swimming again. Another fish I noticed today is slowing down to either the bottom or plants, then rolls sideways and shoots forward, like it has a big itch, perhaps in gills, it looks abnormal and unhealthy. Then there's another fish sitting near the filter pump outlet, sideways in the stream all the time, perhaps not too alarming, but the fish who died did this all the time too. I also notice color intensity of the fish has dropped down a bit. Anyway, I'm hoping someone has ideas on what to do, I'm worried. Tell me if more info is required. I usually feed once a day, allowing them to eat for about 2-3 minutes. I feed them Tetra - Guppy mini flakes. I also use Tetra AquaSafe conditioner with a water change, changing 20% every 2 weeks. I wonder if I need to use more/less conditioner, more/less water changes or give them more/less food. Tab water has almost the same test values, only nitrate is less. I made a video, you can see 2 of the described behaviours.