Urgent! Please Help Me Find Out What's Wrong With My Fish!

[painfullyawkwardsocially]

I will go and purchase a ph and gh test to see how high the levels are, however the water testing strip said that the ph levels for my tank were 6.2 and acidic I guess, and the GH levels or Hardness was 300 ppm or very hard. I agree with you that these accompanied by the fin rot are probably what's harming my fish and will solve these problems quickly. 
 
I also realized that the Hardness of the water was wayyy too high and searched up some solutions. One of them was rainwater, but I want to make sure I don't harm my fish any longer so do you have any suggestions on how to soften the water?

 

[painfullyawkwardsocially]

I've just bought some fin rot medicine ( It's the API MELAFIX ), should I treat for the fin rot first or the Ick? I don't know if it's a good idea to mix medicines or if I can even mix them safely without my fish getting harmed.

I've just bought some fin rot medicine ( It's the API MELAFIX ), should I treat for the fin rot first or the Ick? I don't know if it's a good idea to mix medicines or if I can even mix them safely without my fish getting harmed.

 

[Baccus]

It is a real science to modify/ adjust/ alter fish water to set pH and gH rates. The only way that I know of to be certain of what levels your water is sitting at is to use RO (reverse osmosis) water (lots of fish shops sell RO water for their marine tanks), but in saying that you would still need to test the water regularly and add back some of the minerals that the RO process removed.
I liken it to RO water being 0 or totally neutral, but nothing can live in such water, so the desired amounts of minerals and acids need to be added back to re-add basically the waters building blocks.
There are other methods too but they need more regular testing especially for things like peat moss and drift wood which break down themselves and thus lose their effectiveness over time.