Hi everyone! First time posting and I have quite an urgent health issue!!!

I have two comets that I bought about a month ago. One (pure orange) has always been completely healthy. The other (orange and white) had clamped fins and mouth spasms/head jerk for a few days when I first got it. That cleared up without me having to do anything, and both have been healthy for about 3 weeks. They always have a great appetite and were very active around the tank. They are currently in a 6 gal tank as they are tiny at the moment, but will be moved to a larger tank in a few months when they are a lil bigger.

Yesterday both fish suddenly got sick. The orange and white one showed symptoms first:

*Swimming erratically around the tank
*Strong head jerk combined with mouth spasm: opening and closing mouth rapidly and erratically, shimmying
*Occasional yawning: only saw this a couple of times
*Rests at the surface listlessly, opening and closing mouth
*Fins clamped

The pure orange one was healthy at this point, but within a few hours was also darting erratically around the tank and jerking occasionally (previously that morning he had seemed a bit off, but I didn't think anything of it). Neither fish was rubbing against anything that I could see, and neither had any visible spots of streaks. Both still had a healthy appetite and regardless of their strange behaviour, still would swim excitedly up to greet me at feeding time! There are also six small snaills in the tank that have not shown any sign of illness.

The night before this, I had just done a 20% water change. I re-tested the water when the fish showed these symptoms: pH - 8.0; ammonia - 0.25ppm (can't seem to get it below this point, even though tank has been cycling since February); Nitrate - 10ppm; Nitrite - 0ppm. Temperature is warm, about 81 F, since we've been having a warm spell. I also have a filter that churns up the surface of the tank and adds bubbles, so I wouldn't think that there is a severe lack of oxygen.

I decided to do a large water change since about an hour before the fish got sick my boyfriend inadvertently sprayed some windex beside the tank while cleaning a mirror. I thought that perhaps the windex had contaminated the tank and poisoned the fish, so I changed about 80% of the water. I also took out an ornament that had been losing paint, since I was afraid of lead poisoning. Unfortunately this didn't help, even after about 6 hours.

I did some research and the symptoms seemed to point toward flukes or some parasitic infection. I added the recommended dose of Tetra Parasite Guard (similar to PraziPro; main active ingredient: Praziquantel), as I have heard that there would be no ill effect on the fish and thought it would be worth a try.

This morning, both fish are so much worse and I am afraid of losing them . 10 hours after adding the medication, the fish are showing the following symptoms:

*Very listless: when I woke up both were resting on the very bottom in separate corners and looking ill
*Fins clamped
*Orange and white one has occasional severe head jerk/mouth spasm
*When fish are swimming, either swim listlessly at top just staying in one spot, or dart erratically
*Swimming is a bit wobbly sometimes
*Occasional yawning (only saw this a couple of times)

Both still come eagerly over to me thinking they will get food, so that gives me some hope....... Does anyone have any ideas?? Did the prazi make it worse? Or does the prazi take awhile to work? I can't think of anything else to do!

Please help!!