After hoping that the tank might be problem-free for the foreseeable future as it was well balanced with fish of similar size and temperament and behaviour, a fight broke out this morning. There are occasional daily squabbles but this episode started suddenly, became quite violent and was prolonged - I was working from home and could see them beyond the laptop. Two tetras were swimming in conjoined fashion, covering the entire length and depth of the tank at some speed, then a third joined in. There were “spats” among the silk plants, behind the rock and out in the open. The remaining fish then got involved in their own similar mini battles/chases – the remaining 3 tetras with one another, the harlequins in twos, and anyone (tetra or harlequin) who had the misfortune to end up near the original 3 tetras got driven as far away as possible. At some stage during this episode, one fish incurred an injured caudal peduncle with a protruding fleck very similar to the recurring one that one of the cories had.
I ‘m assuming that this is all about who is claiming the newly available territory previously occupied by the cories and/or re-establishment of the pecking order as it’s very similar to the behaviour when I first got the tetras and the harlequins. Water readings are all good, and fish's colours are all very vivid as usual. I don’t suppose that there is much that I can do about preventing future fights like this although I wondered what thoughts were on the following:
• Indian almond leaves, said to have mildly sedative/calming properties
• Replacing the potentially injury-inducing rock cave with a glass jar cave, an idea I got from an aquatic shop – as fish don’t see the glass of their tank, might this cause potential collisions, especially as decor gets inevitably slightly misplaced during/after weekly tank cleaning?