I have recently started keeping tropical fish and my tank has been up and running for 6 weeks now. I have 6 neon tetras and 7 guppies in a 125 litre tank.
Yesterday all of my fish were lively and swimming around, but when I came down this morning one of my guppies was sitting as the bottom of tank, only moving occasionally. I only have male guppies in my tank so knew it couldn’t be any pregnancy related issues. I did notice a red mark by its gill (see pictures). I went out for about 3 hours came home and the guppy had died. I’m not sure what it’s cause of death was. I was thinking an injury sustained from fighting or something. However, as I am new to this I wanted to make sure that it wasn’t caused by a disease. Please could you guys let me know what you think has happened? Any advice would be greatly appreciated.
Thanks for getting back to me. I had the tank running for 2 weeks then added 6 neon tetras. I took a water sample to pets at home (where I’ve bought all of my fish), and they tested the water and the ammonia and nitrate levels were negligible. They then suggested adding 7 guppies to build up the ammonia levels. That was 2 weeks ago.
I tested all the ammonia, nitrate and nitrite levels this morning and they were all low.
Ammonia - between 0 and 0.5 mg/l Nitrate - between 0 and 10 mg/l Nitrite - 0.5 mg/l
That's a classic sign of ammonia and/or nitrite poisoning, unfortunately. :(
Any presence of ammonia or nitrite is toxic to fish, and it looks as though the poor guppy has been the first to succumb to that. Your readings suggest that the tank is going through the cycling process, having likely had higher ammonia which has since dropped and now resulting in high nitrite. Even that amount of ammonia and nitrite is toxic to fish. (Nitrates are less harmful, and the current level is fine.) Follow the advice in https://www.fishkeeping.co.uk/articles ... ammonia-nitrite-spike.htm
Hope that helps.
Going forwards, in the future, it will be useful to know from your water supplier whether your water is hard or soft, and keep fish whose water requirements match those of your water supply. [Guppies are hard-water fish; neon tetras are soft-water fish. Lifespan of a fish kept in the 'wrong' water is likely to be shorter - but this poor guppy's death is almost certainly as described above.]
OK - the problem is that the tank is not yet cycled. Both ammonia and nitrite need to be at 0 in a cycled tank. Nitrite at 0.5 is actually rather high and given the red gills and red marks which are both signs of nitrite poisoning, I think that's your problem. You need to deal with the ammonia and nitrite by changing water to reduce back to 0 until such time as the tank is fully cycled and they stay there. This article has a lot of tips for dealing with ammonia and nitrite spikes: https://www.fishkeeping.co.uk/articles ... ammonia-nitrite-spike.htm
EDIT: It seems fcmf and I have posted at the same time, but you get the gist - both of us are saying the same
Thank you both for your help. I will make sure to get monitoring those levels. I was advised be pets at home to not change the water for 2 weeks and I’ve been getting advice on setting up from them. I should have come here first.