Ich x long term dosage effects on scaleless fish?

I had some fungus/disease in my tank which killed off some fish right away and corydoras which started flashing as well as ripped fins and slight dusty looking body (velvet?).
I treated with ich x (30-40% daily water change) and after about 2.5 weeks everything seemed fine. No losses, no flashing, and all my corys fins grew back and were pristine. I dosed for an additional week to be sure.
I stopped treatment and in about 5 days I saw two corydoras flashing again and slightly ragged fin edges so I started up treatment again. This time, after another 2 weeks, their fins are looking worse and worse, a lot more ripping and bodies seem lightly dusty again.

Wondering if this is a side effect of so much ich x on scaleless fish and if I should just stop or if somehow there is now resistant fungus/bacteria?
The other fish seem fine, appetite and energy look good for all.

Water parameters tested and good

 

Can you fill out the aquatic emergency template please

 

Sorry for not including, was able to edit once before but cant seem to edit the original post now so will post as comment

Tank
What is the water volume of the tank? 20g
How long has the tank been running? 4 months
Does it have a filter? yes
Does it have a heater? yes
What is the water temperature? 82F/28C
What is the entire stocking of this tank? (Please list all fish and inverts.)
4 Corydoras, 1 glowlight tetra, 1 female german blue ram, 1 bristlenose pleco (2inch)

Maintenance
How often do you change the water? Daily
How much of the water do you change? 30%
What do you use to treat your water?
Nothing at the moment but normally a standard water conditioner
Do you vacuum the substrate or just the water? Vacuum sand

*Parameters - Very Important
Did you cycle your tank before adding fish? Yes
What do you use to test the water? API test kit
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.
Ammonia: 0
Nitrite: 0
Nitrate: 0-5
pH: 7.4-7.6

Feeding
How often do you feed your fish? Daily
How much do you feed your fish?
maybe 1/3 cube of bloodworms daily and wafers/zucchini every now and then
What brand of food do you feed your fish?
frozen bloodworms and hikari mini sinking wafers, zucchini
Do you feed frozen? yes
Do you feed freeze-dried foods? no

Illness & Symptoms
How long have you had this fish?
Corydoras 4 months,
glowlight tetra 2 years,
female german blue ram 2 months,
bristlenose pleco 6 months
How long ago did you first notice these symptoms? 2 months ago
In a few words, can you explain the symptoms?
most noticeable on corydoras, lots of flashing, dusty looking body, fins are jagged and ripped. One cory currently has one little white looking spec on dorsal thats hard to capture in photo
1 longfin cory, 2 rams died early on before treatment (2 months ago)

Have you started any treatment for the illness?
Ich x
Was your fish physically ill or injured upon purchase?
potentially the rams I purchased had an illness, saw one at the store in the tank flash once and was not aware of what this meant at the time.
How has its behavior and appearance changed, if at all?
behaviours seem the same, all eating and have good energy

Explain your emergency situation in detail.
more details in the original post

picture of one of the corys, largest female to show what their fins look like. None really have any other visible signs

 

Ingredients: water, formaldehyde (<5%), methanol (<2%), malachite green chloride (<0.1%)

I don't have to be a chemistry expert or pharmacist to know this is long term a bad idea. Poison, with a sprinkle of carcinogen.

if somehow there is now resistant fungus/bacteria?

Having medicated so long... yeah. At least to a degree this is possible.

 

I don't have to be a chemistry expert or pharmacist to know this is long term a bad idea. Poison, with a sprinkle of carcinogen.


Having medicated so long... yeah. At least to a degree this is possible.

Yeah, I think I was too paranoid of stopping early and it seemed like 1.5-3 weeks was what people were doing. At this point I think I'll just stop treatment and monitor closely and see how it goes.

 

Probably for the better.

 

I really agree with macz on this one. Stop dosing the ichx and with a tank temp of 82 and the fish doing fine other than the flashing and stressed behaviors, just monitor them to make sure the situation doesn't get worse.