In August my daughter asked if she could get fish for her 12th birthday and, although we had zero experience, it seemed like a simple enough hobby so my wife and I agreed.
We went to Petsmart. My daughter picked out three platies and two tetra glofish and a five gallon tank, which they said would be adequate with regular water and filter changes. Everything seemed to be going fine for the first couple months despite never cycling the tank (just set it up one day using API Quick Start and added the five fish the next day).
Then in November one of the tetras, Pete, got sick and died. It seemed like possible swim bladder disease (listing sideways, laying on the bottom of the tank, getting sucked against the filter). Although Pete had refused to eat for several days at one prior point (in Sept or Oct IIRC), he had been acting normal and healthy for quite a while until the sudden illness.
Since we had been told that the fish need to be in schools, we immediately got another tetra Glowfish, Gus, to replace Pete.
All seemed to be going well until this Monday when one of the platies, Poppy, suddenly got sick and died within a day. Poppy exhibited some similar symptoms as Pete (swimming eclectically, listing sideways, laying on the bottom) plus rapid breathing and a curious curved posture. We initially thought she might have been trying to give birth as we had found a single platty fry in the tank two days prior.
Given this second loss, I have been doing a lot of research for the past week and have identified several potential problems with how we have been caring for our fish including:
1) Too few fish of each species (it has been recommended that we have at least five of each)
2) Tank is too small (it has been recommended that we should have at least 15 gallon -- especially if we add 5 fish)
3) Changing entire filter media, which causes loss of beneficial bacteria that break down ammonia and nitrites
4) Using pure RO water (which we assumed would be best for the fish) without re-mineralizing
I'd appreciate input on any of these issues, but my main concern at this point is what to do about #4.
We have been using Tetra EasyStrips (I picked up a an API Master kit this weekend only to find out it does not include assays for GH or KH) and the tank water GH tests 0 (or perhaps 25) PPM at most. KH started between 40 and 80 in August but for whatever reason has gradually trended up to between 120 and 180. pH consistently tested 7.8 with the strips and now tests 8.2 with API master kit.
My understanding is very soft water (low GH) is not healthy for the fish -- especially the platies. What I am unsure about is how to best go about changing it.
We could switch to tap water, but our tap water is softened and also tests GH = 0 and KH = 180 PPM. Our unsoftened municipal water is about 340 ppm GH but is inconvenient to get (need to bypass softener) so I am wondering about just sticking with our RO water (which at least we know is the purest in terms of chlorine and other potentially toxic chemicals) and using a product like Kent R/O Right which probably has the best mix of essential minerals vs. whatever happens to be in the municipal water.
And regardless of what approach I use to raise GH, what it the proper rate of increase so as not cause a pH swing or otherwise stress the fish while at the same time not delaying the needed correction too much?
I'd appreciate any expert advice I can get... Thanks!