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My Corydoras Paleatus have all been scratching themselves against obejects for around 2 months now.
They seem to scratch their gills in short bursts, maybe 10+ times an hour.
Over the last month the scratching has increased in freaquency and seems to be affecting more Cories.
There are 10 Cories (2 adults , 8 juviniles) and 6 white cloud minnows in a 60cm (50L) bare bottom breeding/fry/grow out/ come-hospital tank.
Filtration is via a power filter resun 700 and large air sponge filter.
The adult cories and minnows were scratching/flicking before they were moved into this thank.
They have all been in this tank for atleast a month now.

The tank recieves daily water changes of 30-50%
the ammonia and nitrite are 0, nitrates are kept below 30ppm
temp: 22-23*C
ph: 7.5

No outward signs of disease; no white spots or bumps,gills a health red colour with nothing attached to them - that i can see with naked eye, no major signs of laboured or fast breathing, fish does not have a velvet appearence.

Fish are feeding well on combintaions of, crushed flake, shrimp pellets, algae wafers and spectrum growth formula.

My first educated guess was some sort of parasite. (gill flukes)
Treated tank with praziquantel @ 200mg (2 tablets), repeated 7 days later @ 250mg.
Fish have shown little or no sign of improvement I have seen most of the cories still flicking including the 2 adults and some of the smallest juviniles.

The two adult cories have succesfully spanwed on a number of occasions.


Hours of googling has netted anything from white spot (there are no white spots on my fish) to velvet ( no velvet appearance, besides my fish prefer silk) to internal bacterial infections.
My fish specifically only scratch their gills and no other parts of their bodies. Searching for gill scratching or flicking and other combinations , has really not provided the solution.

I'm hesitant to treat for all the possible things gill scratching could be and am aware that cories can be sensetive to some meds.
I guess if I can nail the exact cause and treat it that would be ideal, but also if there are any suggestions on a multi-cure that the cories can handle and isn't too rough, I might try that.

thanks

Hi Cory and Dory,
I've had exactly the same problem with my cory tank. Water parameters were always fine, 0ppm NH3, 0ppm NO2, <10ppm NO3, pH7.8, not sure about hardness. There were no visible signs of infection. Spent months doing plenty of water changes and treating with melafix, no effect.
I think I might have sorted it now but not sure exactly why. First I reduced the fine gravel depth from 1.5" to 0.25-0.5", thinking that anaerobic substrate might be the problem (I know you have a bare bottom tank). At the same time I put activated carbon in my filter (the carbon foam pad in a fluval2+). It's now a week later and I haven't seen them scratch for 5 days. They used to scratch all the time even though they carried on their usual active business. I appreciate the problem may come back but 5 days of no scratching after intermittant scratching 24hours a day is encouraging.
When the carbon expires and i have to take it out it'll be interesting to see if the problem comes back, if it does I'd guess something in my tank is altering the water chemistry to ill effect. It's decorated with pebbles (assured safe from retailer, bogwood and anubias, jave fern and 2 terracotta pots).
Hope this is of some help.
Good luck, let me know how you get on.
Pete.

how are your cories doing now? still no flicking?
i use a product called geo liquid, it pretty much does what carbon does in the form that it bonds to all contaminants organic or chemical and sinks to the bottom, where it is bound indefinetely.
i'm a curious sort of guy, i'd want to know what exactly the carbon is taking out that is making the cories sick. I'm very sure that whatever carbon can take out so can geo liquid (maybe apart from water discolouration.)

I have a pretty strong feeling that whatever it is, it could be contagious, as the juviniles were not showing any flicking behaviour until after the adults moved into their tank and the water conditions according to my kits and general observation in both tanks were very good.

i have ordered some broad spectrum anti-biotics, but i'm holding on to them with caution as i dont want to jump too swiftly on the medication band wagon.

if i were to go down the list and treat for all disease that could cause the gill flicking where shoudl i go to next?
i've treated with pranziquetel (for flukes and external parasites) with no improvement
i've treated with melafix
and now i will have antibiotics (Tetracycline Tablets)

i think most sites says scratching is realted to white spot, but there are no white spots grains, anything on the skin of my fish.

what meds shoudl i defintely stay away from?
formalin?
malachite?
copper?

anyway they are not getting any worse, but i dont want them to get worse just because i didint know what to do.


thanks for your help