trouble with Platies

Question
We have a 10 gal tank that is about 3 weeks old, unfortunately we got the aquarium without much research and bought the tank and 8 platies at the same time so we couldn't let the tank establish first.
Day 2 we lost our 1st platy. but since then no problems until yesterday, the fish were hanging out at the bottom of the tank not swimming much, and we lost platy #2 I did a 50 water change, I used  AquaSafe water conditioner in the new water, the fish started swimming like they did when we first got them, then we lost #3 today,  1 platy is hiding in the fake log stump, 3 are at the bottom of tank around the roots of the tall grass plant and 1 is swimming up and down under the filter.  also one of the fish by the tall grass has a cloudy eye. ( all plants fake)
I tested the water with a  API 5 in 1 test strip I think the GH is at 120ppm (6.7 dGH) KH is 180 ppm (10 dKH)ph is 7.0 Nitrite is .5 and Nitrate is 20 but I'm having trouble figuring out what numbers are good for platies.  Can they be saved?

Answer
I would suggest a 50% water change daily until the nitrite levels are below .25 ppm and whenever the nitrates get above 10 do a water change.  You tank is going through the cycle.  What are your readigs for ammonia?  Ammonia is formed first, and is broken down into nitrite by a certain form of bacteria, from there nitrite is broken down into nitrate by another bacteria, and nitrate is removed through plants (live) and water changes.  The fish with the cloudy eye is likely sick due to stress and ammonia/nitrite poisoning, which can be helped with frequent 50% water changes.  For the next week or two, I would def. suggest keeping a close on on the water levels and changing water when ammonia is above .4, nitrite .25 and nitrate 10. Platies are usually pretty hardy and do well in a pH of 7-8.5 which medium to hard water, so your water is fine.  Once the nitrogen cycle is over, you should find it much easier to keep fish.  You are about half way there now.  Good luck and let me know what happens!