I have a 4 ft planted tropical 'community' tank in my living room, containing honey & pearl gourami (2 of each), platies, guppies, a pair of bristlenose catfish, six Styerba's corydoras, 3 dwarf chain loaches, and half a dozen of each of neon & black neon tetra's. Up until last week I also had half a dozen glowlight tertra's until I lost four glowlights on the same day - and I can't quite work out why!
I regularly test my tank water weekly, using the Tetra 6-in-1 test strips and the Tetra ammonia test kit. Up until a month ago my weekly test results had been as follows, consistently, for a couple of months:-
Nitrate 0
Nitrite 0
GH 16
KH 20
pH 7.6
chlorine 0
ammonia 0
A month ago, in mid-May, the pH shot up to 8.0 and last week and the week before the nitrate level also shot up, from 0 to 10. Three days after the nitrate level rose to 10, I lost a platy and a glowlight tetra with no aparrent symptoms showing previously - they were just DEAD when I came downstairs in the morning. I did a partial water change of 4 x 12-litre buckets. Two days later, on Tuesday of this week, I came downstairs to find 4 glowlight tetra's dead leaving just two glowlights left in the tank.
When I tested the tank water this afternoon the nitrate level was still at 10 and the pH had risen to 8.4, the highest its ever been. I know we live in a hard-water area but 7.6 is the normal pH for my tank and I haven't the faintest idea why it should suddenly have increased. I did a 50% water change in my tank (10 x 12-litre buckets) and a couple of hours after the water change the nitrate level had reduced to a much healthier level of NIL and the pH had reduced to 8.0.
I change the filter pads regularly in accordance with the manufacturer's schedule (Juwel), always use a water conditioner when I top up the tank water levels, and all the other fishes in the tank appear in the pink of health. I really am puzzled as to why I lost four glowlights on the one day - can any forum members throw any light as to why this may have happened? Did I do the right thing in doing the 50% water change today? What can I do to make sure this sort of thing doesn't happen again?