Hello, I've been fishkeeping for 4 years now. I have 2 tanks and currently have a problem I can't figure out in one. I'll start with my specs: 57L -4 Crossocheilus Siamensis (Siamese Algae eater), 2 of 11 cm, 2 of 5 cm. -4 Thayeria Boehlkei (Penguin Tetra) - Planorbis sp and trumpet snails in low numbers -Heavily Planted: lots of anubias, some hygrophila polysperma, some java fern. - Driftwood since it started: same piece of driftwood. - Gravel substrate - No CO2 - Avg Temperature 26ºC -NH3 and NO2: 0 -NO3: usually 100mgl before waterchange, 50gml after waterchange. It's tough to get it lower since out of the tap its 25mgl. -PH: I don't remember, havent checked in years since I can't change it, but I remember it was fine... like 7. I'd rather keep it stable rather than try to force it and be unstable. I went on a little vacation, leaving the house alone for 2 and a half days. This morning, after returning, I go to check this tank to find the my 2 big Siamese Algae Eaters in the bottom, barely moving. One of them is sided and only breathes, the only moves ocasionally only to stop resting in some anubia roots, without moving much. I can't find one of the smaller SAEs that I have. All penguin tetras are behaving normally. I haven't added anything to the aquarium since like 2 years ago. Manteinance is regular and normal, nothing has changed. What could be the issue? I just did a partial water change to get the NO3 to 50mgl (monday is water change day). I added an ir bubbler to get more oxigen in the water in case that helps. I added SERA Toxivec just in case. Sometimes we do the water changes with SERA Aquatan, sometimes without. Any help will be welcome, I'm desperate. Thank you and greetings from Chile.