Strange tail-decay in Pleco fry.

[Zeaqua]

Hi all. About a week ago, I lost a few Pleco fry, and soon after many, MANY more had passed. I was devastated. I had assumed I had an ammonia spike, so I did several water changes, and afterwards, ammonia tested at 0. Still, I lost plenty of Plecos. At the time of writing this, nearly all of the fry have died. Yesterday, I noticed a white patch on the tail of one, and assumed it was columnaria, which I had experienced with neon tetras before, so I dosed API general cure. Today, I noticed all of the plecos have nearly translucent tails, and here are some photos. Any advice would be appreciated. My parameters seem fine, with 25ppm nitrate (with plants), 7.6 ph,  and at 76f.

[jwcarlson]

How often are you changing water?  25 nitrates is pretty high for fry raising (at least in my opinion).  

[Zeaqua]

I usually change about 3x a week, but since this started, I’ve been doing it once or twice daily. I haven’t changed water for a day bc of the meds I put in.

[Colu]

It could be a bacterial infections api general cure isn't effective at treating columnaris one of the active ingredient metronidazole does treat aeromonas that a gram negative bacteria most effective treatment for columnaris i have is  kanaplex and jungal fungus clear fizz tabs containing nitrofurazone following this treatment plan  fry are more sensitive to medication so I would a course of kanaplex and add some Indian almond leaves as they have antibacterial and antifungal properties you might have to add one leaf per gallon to get a beneficial effect keep a close eye of your water parameters and add an extra air stone during treatment@Zeaqua