I'm so stupid! >.> My platy already attacked and killed my other platy and I never would have thought of checking the attacking platy if it has diseases. The platy might have had the disease for 1 and a half month since that was the time he killed my other platy.

I was sick today and decided to just look at the aquarium all day and after a few minutes I noticed he had dropsy and was attacking my guppy. The platy only has dropsy and my guppy and corydoras doesn't show any symptom. The dropsy doesn't look very bad right now. He doesn't have a bulging belly but has the pin cone like scales although they are not sticking out as much as the pictures I've seen. He looks like he's bulging a bit on the left though.

I have fungus clear tablets but I don't have a spare tank and filter so I can't make a quarantine. I have very little money as well since I'm only a kid.
Water Parameters right now are
0
ammonia
0
nitrite
?
nitrate
Sry I don't have a nitrate tester because my
test kit doesn't come with nitrate! I did a
water change yesterday and I always do it once every week and sometime twice if my tank looks dirty.
Please help quick! My guppy is being attacked right now and I want this to stop.

I've had him since he was smaller then a inch.
Please help me or I might have to euthanise my platy because my guppy and corydoras might end up in my back yard if I don't fix this quick.
