Incompatible medicine? Dead rice fish, white growth

[TioTeo]

This morning I noticed a small white growth (pin head size, on back flank/side) and a single spot (pin point, top base of tail fin) on the sole Medaka rice fish in my 5.5 gallon quarantine tank. (Sorry no pictures as she is dead) [similar to one of the growths on Bettas in this thread.]

 

I thought it might be ick as I had previously treated the tank (three cardinal tetras had a few pin point spots) after shipping three weeks ago. But they were treated and have been fine since. (The rice fish also arrived in that shipment, but we’re placed in their own indoor pond.) 

Possibly related details: I received four rice fish (3 female, 1 male) in my indoor pond three weeks ago and they were happy and healthy and immediately started breeding. I, unfortunately, went on vacation one week after receiving them for two weeks. They had automatic feeders and an air stone (no filter), and someone checked on all my fish (20 gallon, 12 gallon indoor pond, and two other 5 gallons) every few days and everyone was doing great. I did 30% water changes immediately before leaving and as soon as I got back. However, the sitter did not notice that three of the rice fish were missing, presumably dead. I did not find their bodies in the tank anywhere in or around the tank (or in my roomba) so I assumed the lone surviving female (or the numerous rams horn snails) must have eaten them. However, there were approximately 75-100 happy little fry. The lone female was chasing them and nipping at them, so I decided to move her with the other quarantine fish while I set up a second pond. 

She was initially being chased and nipped at for a few hours after transfer by a quarantining female betta who had been treated with levamisole for internal worms three weeks prior in the quarantine tank. So I decided to move that female betta back out to the community tank, as she is doing well and getting her white color back. 

It has been about 5 days and she was a little shy, but seemed fine, along with the other four new cardinal tetras (treated for ick previously) and three new French blue star endler tetras, when this morning I noticed the growth. She is a platinum rice fish, so it could have possibly been there a few days and I had not noticed, but unlikely as I was checking in on her everyday to make sure she was adjusting. 
 

Possible error in treatment:

In order to cure what I thought must be ick, still in the tank from the previous fish, I treated this morning with Super ick cure (API), only 2.5 ml (recommended 5 ml/5 gal), and then after questioning if the white growth may be a bacterial infection I decided to treat with 1 ml (recommended 1 ml/ 10 gal, admittedly, this was a little high) of Melafix (melaleuca oil 5%, API). There was no activated carbon in the tank, and the tank parameters when checked this evening were: pH 7.5 (normal), ammonia: 0 ppm, nitrite: 0.25 ppm, nitrate: ~7.5 ppm, KH: 40, GH: 30. There is not temp gauge in the tank, but the others read ~80 F, and the high today was only 84 F (outside). However, my three nerite snails were all on the bottom of the tank looking in bad shape (I transferred them to the new pond to see if they would recover), but none of the other fish (3 endlers and 2 tetras) were having issues nor any of the many rams horn snails (adult and new hatchlings). 
 

I have done a 50% water change just to be sure it is not going to harm the other fish, but I am uncertain of the possible cause. 
 

Are Super Ick Cure and Melafix incompatible medications to be administered together? Or do you think this is likely the same thing that killed off the three other rice fish previously? 
 

Any thoughts on possible causes, and things to look out for in the other fish in that tank? And/or thoughts on possible conditions that may arise in the rice fish fry as they grow up from the previous pond?

 

Thanks for reading this murder mystery…

Edited July 14, 2021 by TioTeo

[Colu]

Does it look small grains of salt.on your fish if the answer yes it definitely ich I would just treat with API super ick cure  am not sure whether you can mix those meds together super ich cure should be used at half dose if you have snails in your tank

[TioTeo]

Update: I think it was incompatible chemicals and concentrations. My nerite snails, moved out of the tank, came back just fine. 
 

i also realized that the Melafix was pond Melafix, which is significantly more concentrated. In accidentally doubling the dosage I added way more than would have been added had it been the aquarium dose. 
 

I think the loss of the other rice fish the previous weeks while gone may have been a. Fluke or bullying. The baby fish in that indoor pond are still growing strong.