Scratching discus only after water change

[Finman]

I would appreciate any ideas you may have to help figure out why discus scratch after a water change The replacement water is from a RO unit that is aged in a large plastic container. The PH is identical along with the same temperature. In the main tank there is no ammonia or nitratites The PH is 6.75. The scratching certainly is something that is an irritant I originally thought gill flukes or some other parasite and have treated with Paraguard for 21 days and API general cure. The color of the fish are good along with a great appetite. The scratching normally goes away in 24 hours I do 30% WC twice a week. I would appreciate any suggestions or help

Thanks in advance

[FishFanMan]

I have no idea but what size tank do you have and what's in it? After the med treatment did you do a very large WC with RO water? Maybe add the new water slowly during WC? What's your TDS reading in the tank prior to WC? Perhaps the difference in osmotic pressure is causing a tickle to the fish?

[Megalodon]

Chlorine/chloramine in your RO water?

[Finman]

My tank is 50 gallons with a pair of tiger turquoise My CM level is higher in the tank because of buffer and the stress coat I treat them with. I thought the chorine would be taken out by the RO unit? I have gravel and a few pieces of slate rock no plants. I have a canister filter and the temp is 85

Thanks again

[LizStreithorst]

Chlorine will be taken out by the carbon filter. It will take destroy the RO membrane if you don't change the pre filter often enough

[Megalodon]

I thought the chorine would be taken out by the RO unit?

I had to add several extra catalytic carbon stages before I got undetectable chlorine. It doesn't take much to harm fish so you need a test that can read down to 0.02 mg/L.

Chloramine will pass right through an RO membrane. Not sure about chlorine but either one will damage the membrane and once it's damaged enough it will definitely be passing through.

[Finman]

Thank you

[Dee1958]

I would appreciate any ideas you may have to help figure out why discus scratch after a water change The replacement water is from a RO unit that is aged in a large plastic container. The PH is identical along with the same temperature. In the main tank there is no ammonia or nitratites The PH is 6.75. The scratching certainly is something that is an irritant I originally thought gill flukes or some other parasite and have treated with Paraguard for 21 days and API general cure. The color of the fish are good along with a great appetite. The scratching normally goes away in 24 hours I do 30% WC twice a week. I would appreciate any suggestions or help

Thanks in advance

I would say it's chlorimine as my synodontis are very sensitive to water changes until I add the water treatment, right now I'm using am quell. Dee