I did 3 50% water changes over 3 days and have done 25% one everyday for the last 3 days as advised from the fish shop I go to, i think I figured out how it spiked, I wasn't using the gravel vacume correctly so when got that going right there was a lot of build up in the gravel. I have a 70l tank, with 4 guppies, 3 platys, 2 mollies, 1 glass catfish, 1 flying fox and 12 neons, 10 of them school well and 2 seem to keep to themselfs more often. I have had fish in the tank for 3 weeks, it was cycled for 3 days short of 1 month. I have had one death of a guppy (which was devastating for me) but I noticed and got it out if the tank within half an hour of seeing it swimming to despairing and finding it dead in the plants. I use prime as conditioner and added stability when I was doing the 50% changes to drop nitrate levels. It's a aqua one eco style 61 tank which came with the filter so I don't know much about the filter sorry. Test kit is aqua one liquid test kit I have been working closely with the fish shop to determine and double test levels in my water but his advice to a sick fish is to just flush it which I am not ok with if there is a chance the fish is actually ok