Grey/white patches plus flashing?

Tank Info: 29 g, well-planted, cycled, with Aquaclear 50 filter. Contains 5 SterbaI cories (will get more when they come into the store again, and will quarantine them before adding to main tank) and some pond snails. Most recent test with API liquid kit showed 0/0/5; GH and KH of about 2-3; pH of 6.5; temperature is 77F. Substrate is EcoComplete topped with soft sand, though some larger pieces of gravel have made their way above the sand. It's been set up for about two months, but fish have been there for about two weeks.

Tank gets fertilizers; Flourish Excel about 3x a week and Flourish, Iron, and Potassium twice a week. Prime used to dechlorinate and neutralize the tap water's .25ppm ammonia until the filter can deal with it. Water change of about 20% once a week for now.

Problem: One of the cories got a patch of lighter grey across his face about a week ago. Patch stayed the same for a few days, then one of the other cories also got a small patch of it. It's now progressed to be whiter, more wide-spread and patchy, and, most confusingly, the two of them have started flashing/glancing. I've been treating with PimaFix for four days now, though it doesn't seem to be making any improvement, so I'm trying to research what to try next, but no symptom list has both the patchy fungus-or-bacterial-infection stuff and flashing. I haven't noticed any ich spots or parasites, but I'm keeping a close lookout on them. Should I treat for fungus or bacterial infection? What would you use to treat it?

Images
Day One:




Day Six?




Edit to add: Otherwise, their behavior seems normal for what they had been doing before. They're eating well and similarly active as they were before this developed.

 

Welcome to the forum

What are you feeding them?
DoubleDutch might be able to identify what could be wrong.

 

For feeding, it changes - about every other day, Omega One's community blocks* (broken up into smaller pieces so they sink and so I can control portions, because they can't eat the whole thing at once!); on off days, rotated between frozen mysis shrimp, frozen brine shrimp + spirulina, and frozen bloodworms (no more than twice a week). I've tried feeding them shrimp pellets and algae pellets a couple times but they don't seem to be able to/understand how to eat them, so I've given up on that for now. Some sources say they're omnivores, others carnivores, so I'm trying to find more info on that.

One fish has also developed a swollen eye. TC Tetracycline seems to cover the symptoms, so (after significant effort - little things are fast!) I've moved them to a hospital tank and I'm gonna give that a go, unless someone has other suggestions!

*Ingredients: Salmon, Halibut, Pacific Cod, Whole Pink shrimp, Black Cod, Shrimp Eggs, Gel Binder, Vitamins (Vitamin A, Vitamin D, Vitamin E, Menadione, Thiamine, Riboflavin, Pyridoxine, Vitamin B12, Ascorbic Acid, Niacin, Pantothenate, Folic Acid, Biotin, Choline, Inositol), Garlic.

 

Today was day 3 of tetracycline. It hasn't cleared up completely on Porkchop (the most patchy of the lot), but it has not spread further and I do believe it has actually receded a bit. I'll keep on with the tetracycline for another few days, though the water changes are getting annoying. x.x Keep your fingers crossed that I've hit on the right meds for this!

The hospital tank isn't cycled, but apparently this medicine can sometimes kill a cycle anyways. Our tap water has .50 ppm ammonia. I've just been taking water out of the hospital tank, tossing it down the drain, taking the same amount from the big tank (which *is* cycled and gets water to 0/0/0 because of plants, yay) and using that for the water change, plus Prime to keep the remnants of ammonia non-toxic.

 

This looks like a case of chilodonella or trichodina(lla).
Ich-like parasites that irritate the skin (flashing). Try to treat with an antipatasital med (mors Ich-meds will work). The fish in the first pic is rather thin. Could be there is an underlaying issue causing this issue (worms ?).

 

Tetracycline is only useful for popeye/ eye cloud Gram + Strepocaccus bacteria.
Just so you know for future reference, its not gonna stop any disease outbreak.
There are two diffrent types of bacteria that make fish sick, gram + and gram -, the only fish disease I know of that is gram positive is Strep bacteria that cause popeye,eye cloud ect.
All the fish disease that cause tail rot or skin lesions and death are gram -
Tetracycline is a gram + antibiotic, and a really bad antibiotic, in fact it is more likely to kill off ALL of your good bacteria than actually kill any disease-causing bacteria in your fish.
I agree with double dutch, you need to treat the underlying cause of all these symptoms, there seems to be a good course of action.....
1 Figure out weather its columnaris bacteria, or a skin parasite called (costia)
2. Check for any smpotoms of worms, usually a red thread like a paintbrush coming out the fishes anal vent
3. Use the CORRECT medication
Subjecting fish to combined meds, or incorrect meds, can cause additional stress on them and kill them, and ruin your tank, while the actual disease or parasite continues on to kill the next batch of helpless fish.
4. Re-establish the Main tank- Get your display tank setup again, get the water clean and healthy looking, make sure there is no ammonia or nitrite
5. Listen to the advice on here, not the pet store ppl
Some of us on the forums are pretty good believe it or not, and we WILL give you loads of better advice then any petco part time fish employee with one tank of goldfish at home would.

 

Thanks for the info, you two! One of the fish had developed a swollen eye, which is one of the reasons I made the move to get medicine, even though I didn't have a clear diagnosis.

I'll check for parasites and research more on the specific ones y'all mentioned. The bare-bottomed hospital tank will make this so much easier! There has not been much flashing, and it was a very late addition to the symptom list. Would you still suspect external parasites over bacterial infection?

If it were columnaris, I would probably have seen deaths by now, right? It's been well over a week (probably two) since the first symptoms appeared, and columnaris is infamous for quickly racking up a body count.

I've been maintaining the main tank's cycle with nothing-added ammonia so that it's ready for the fish when they're ready. I've also been using it to turn my tap water's .50 ppm ammonia into 0 ppm ammonia to use in the hospital tank's water changes - is there any reason not to do this? I figure the main tank is either already infected with what they have, which the medicine will hopefully treat, or is not infected and therefore safe to use.

(And totally agree on the pet store people...not many fish knowledgeable ones in the big stores, though I know they exist, somewhere - and even in the LFS, the employees I've spoken to have been in the dark ages. "Oh you can't cycle a tank with ammonia - you need to take a couple dozen feeder goldies, stick 'em in there for a week, then bring them back and you can take home any fish in here. You need the fish waste to age the aquarium!" Umm, yeah, no thanks!)

 

Yes, that is not a columnaris skin lesion. Look up costia and those parasites dutch mentioned, and try walmart for "parasite clear"
It contains acriflavine, an antiseptic, and malachite green, a paracide.
Maybe those parasites are killed by something diffrent? idk I'm just saying read up on those, and if they can be killed by a simple ick med, or something special like copper.