Hello all, I am brand new here though I have had fish my entire life. Up until now I have not had any major problems or illness problems with fish. Last weekend I went to the pet store and bought a couple of new fake plants, new filter cartridge, and a new heater as my previous one had stopped working about a month ago. The temp in my house had been OK and the fish were perfectly fine during the time. So Saturday evening I had to empty a little more than half of the water because we had to move the 10 gallon tank to another room in our house. I did not even think to save that water and now I am highly regretting it. I cleaned out the gravel a bit, and then added new same temp water to the tank, added the same chemical I always use to "make the water safe" it dechlorinates etc its Tetra brand and says it contains bio something and its a yellow bottle (sorry I'm not at home right now to look). I added the newly washed fake plants and the new heater washed as well. By wash I did not use soap as my dad who always told me to always only use water when I clean the aqaurium parts. I put the heater to 70 and made sure by keeping an eye on the thermometer as well. THIS IS WHERE I am told I also went wrong by not gradually raising the temp since they had been in about 60 degree water while the old heater was inoperable. I rinsed the new filter cartridge as the old one was very very dirty with slime etc. Once again something I've always done as I had been told to change it out once it is done. All seemed fine. They were playfully swimming etc. Sunday I leave to visit family for Easter. Sunday night one fish floating and ALL guppies in the tank are near the top, listless, uninterested in anything, and their tail fins are all POINTED? They had been just fine on saturday. A trip to the petstore last night (monday) and they seem to think it is a fungus of some sort or a fin rot disease. So I buy this dissovling tablet thing that it supposed to rid my tank of this. I got home and use a water test kit and found that the PH was off the charts...mine only shows up to 7.8 and it was about 2-3 shades darker than that. I added PH Down tablet. I then added the med tablet, which turned my tank's water green and then waited and watched them the rest of the evening before heading off to bed. This morning two more were dead, and another nearly dead and unable to swim. I put him in a net inclusure near the surface so he wouldnt be swooshed around the tank by the filter current and because I had to leave for work. Now there are I think 2-3 adult guppies left, and two smaller babies (not tiny like fry, but about the size they start getting colors) of which are the only two that ate last night. I had put in a small amount of flakes to see if they would eat. There are also two small skirt tetra's of which do not have any fin damage, and are swimming ok, but they are not eating and are a bit listless though not nearly as severly affected as the guppies. I have no idea what to do now other than just wait it out. I will test the PH again when i get home later today to see if the tank needs another ph down tablet. As for the meds it said to wait 3-4 days before adding again if needed. I feel so bad for my little fish. I have had them all about a year, raised from fry. What should be my next step, should I completely give up hope? I don't know all of the fancy terms for cycling a tank but I have a feeling the huge water change is what started this, or that there was something weird in our tap. That's all I can guess because their fins were long and pretty before.