At A Complete Loss, Fish Flashing

Hello all, I have posted on this issue a couple times but now I am at a complete loss. In my 20 long I had 10 pygdmy corys, 3 peacock gudgeons, 8 harlequins and a peaceful betta. Tank is established and has steady reading of PH 8.0, Ammonia 0, nitrite 0, nitrate below 5 ppm. Water is slightly hard but nothing crazy. The pygmy's began rapidly dying off, betta suffered major fin loss (not fin rot) and my gudgeons were flashing like crazy. This started about 3-4 months ago and during those months I have (separately) dosed API General Cure, Furan-2 and Kanaplex, back to back Prazipro treatments and then Paraguard. The pygmy corys all died pretty quickly making me think I had aggressive columnaris, my bettas fins are now slowly regrowing, however my gudgeons continue to flash fairly frequently and every once in a great while I'll catch a harelquin flashing as well. I do 30% water changed twice weekly. I am just totally and completely stumped as to what could still be causing them irritation.

 

So one other thing that may help with irritation if you feel like it is a methylene blue dip, which can help with both infection and accute toxicity of certain heavy metals, toxic forms of nitrogen, etc. I think I remember commenting on a previous post of yours. This does seem pretty unusual, so maybe you'll have to consider basically a complete disinfection of the tank, including the filter and all. Also on the off chance there is something wrong with the water, is it at all possible for you to use pre treated water?

 

I think the most common cause of flashing is ich. How thorough was your Paraguard treatment? Did any treatment seem to reduce the flashing? Ich can hide on fish without an obvious outbreak of spots covering everyone so I wonder if it's just ich coming back again and again (it's very hard to completely eliminate).

Lastly, have you used Excel or anything similar?

 

I think I'm going to give methylene blue a shot. Everyone in the tank is looking great and acts just fine and eats well. But the flashing persists. What exactly do you mean by pre treated water? Do you mean something like putting water in a container, using prime and running an airstone/heater in it for awhile? that could be arranged....I have also looked for signs of ich but over the course of 4 months have never seen any visible symptoms. I was very thorough with all treatments but I stopped paraguard on the 6th day opposed to the recommended 7 days. After seeing flashing throughout all treatments I figured one more day of paraguard won't do any good. The only time I remember seeing slightly reduced flashing was when using kanaplex or apI stressguard. I don't know if it's my imagination but I think the flashing increased at the start of the winter, I live in Vail Colorado high up in the mountains so I'm fairly sure the towns water source changes from winter to summer. I just don't know what else to test for in the water that could be causing the irritation if it is a water source problem. I was using Excel, Flourish Comp, Flourish Iron and Flourish Potassium but have not been dosing excel or other ferts during the medication processes. I also use DIY Osmocote root tabs...my substrate in places is only 1.5 inches deep or less could the root tabs be leeching into the water column causing irritation?

 

I mean like water that a company has pre treated. I know you have 20 whole gallons, but I figured I might as well ask. Also do you use city or well water? I doubt the root tabs are an issue unless you have a gazillion of them, but you could always try removing them and seeing what happens. If there was anything else in the water, it probably wouldn't be safe for people either, which is why I don't think it is the most likely problem. Unless you use well water maybe. Also, did you do the whole time length required for each treatment?