Thanks for the replies so far. I haven't added any chemicals or new pieces of wood but there are red flakes in the food. I think I'll assume that's the cause - I've ordered a new filter element just in case though and I'll switch food and see what happens before I introduce any new fish. :)
Roughly its about 3ft by 1ft and about 18" deep and after my recent fatalities I have the grand total of 2 tiger barbs and 2 silver tip tetras!!
I have checked Nitrite, Ammonia and Nitrate and nothing seems out of the ordinary.
Can anyone give me any idea why a newish foam filter in my Biolife filtration system has gone bright red? It seems to have taken about three weeks to go from its normal colour (greenish) to bright (scarlet) red. I have just lost my favourite fish - a red finned shark and I am wondering if...