Hi I am new to having an aquarium. We got a 20 gallon freshwater tank in July. Everything was good until about a week and a half ago. We currently have a balloon molly a dalmation molly and a guppy (orange and yellow). There are also 3 babies in there. We lost a molly last week and our pleco today. I have 5 in 1 test strips and ammonia test strips. The water has been fine this whole time (per the test strips) until about a week and a half ago. We left a friend in charge of the tank for a few days while we were away. Came home to food everywhere so we did a good cleaning... about a 30% water change or so. Since then the water quality has gone bad... ammonia was high and it seems to be ok now but the hardness is low ph is low and the nitrates and nitrites are way too high. The aquarium store gave us something to raise the ph and quick start. She advised to not do a water change for a week or 2. The dalmatian molly is swimming weird now and his eyes look cloudy and swollen. What should we do? This is very upsetting.