I have a 40 L tank with 8 neon tetra, 2 glolite tetra, a small sucker fish and 8 or so guppys (majority are males), laterly Ive noticed that one one of my guppys and only that guppy has been getting bite marks on his tail, his relatively new and has only been in the tank 2-3 weeks more. I’ve never had this problem before but Im pretty sure its the neons doing it, the problem is I got no idea how to get them to stop. Oh and it started about a day after I started adding a small amount of this stuff to reduce the PH levels of the tank a little each day.
Im lowering the PH because my guppies tail started dulling in colour colour, I noticed with 2 new guppies a couple weeks back that 2 days after adding them their tails had gone from blue to black and developed an odd, sorta transparent outline kinda thing round his tail, the 2 guppies I had orginally developed this over time. The neons also developed a reddish sort of colouring around their tail, I tested the PH and it was nearing 8 so I decided to lower it.
Sorry I meant to put for the neons the red patch was around their gills, not tails.
Most noticably a guppy I have who has a white tail developed a sort of browny black patch on it thats looks almost like dirt. However since I started lowering the PH the fish do seem to be getting noticably healthier, the neons dont have the red bit round their gills and theyre shoaling better.

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