Some local fish store will test your water for a couple dollars but I would recommend investing in some test kits ick X might cause some discoloration I would try API super ich cure and salt at 1table spoon for 2gallons
Decorative rock could be leaching mineral puting up your pH and kH removeing mite lower your pH and kH you could put almond leaves in and more bog wood to leach tannin to lower you pH