Are these fish new, newer? Have you added anything new, plants or fish or snails in the last month or 2.
Tank in gallons would be appx 14G. (for others who use G)
Regarding the water test, did you check for ammonia?
If so what was / or presently is if you can measure it again...
aka general hardness / calcium/ carbonate hardness/ alkalinity
How often are you doing water changes, and is there a filter and how much water are you changing?
Are you familiar with the nitrification cycle?
If not read, the link in my signature which will review some helpful information for water keeping.
Are there salty looking speckles on the fish, the spot on the Guppies head looks like something other than Ich?
**copying basically the same thing from my other thread answer.
If it is Ich / more salty speckles on the fish, here are a couple articles
I would do 2 PWC
's about 30% one then another, perhaps your tank does not have enough BB to handle the bioload.
Try lightening up on the amount of food you feed and read the article in my signature, for more insight and this might help too.