Originally Posted by scott36854
What size tank do you have?
What kind of filter?
Have you only had the platys and swordtails?
If it keeps happening then your water is contaminated possibly.
How often do you do water changes? When was the last one?
What are the water parameters if you don't mind posting? If you don't have your own test kit I would recommend API Master Test Kit.
Also, what kind of plants do you have in there?
Are your fish Flashing? Do they have clamped fins?
Under the Tropical Fish Diesase under Important links there is this page with this information. I think this is what your fish have: Bacterial Fin Rot
The fins are frayed and getting shorter. Edges are whitish.
Overpopulation, severe stress especially on transit, untreated injuries, poor water quality and poor maintenance are the main causes of fin rot. Fin rot can occur in connection with columnaris, fungal overgrowths, lesions and as a secondary infection to parasite infestations. Ffish begins to have difficulty swimming due to the damaged fins.
Broad spectrum antibiotics, frequent water changes are a must to improve water quality
Read more: http://www.tropicalfishkeeping.com/t...#ixzz1pgSrpRoz
This is another possibility but the Bacterial Fin Rot is more likely because of your description Osmotic Shock
Detachment of mucous membrane, fins appear to have been blown off, internal diseases become the consequences, increased vulnerability to skin diseases, gill and fin rot.
When fish is transferred from water with high conductivity (high salt content) to water with low conductivity without an intermediate phase for adaptation, they suffer from osmotic shock. The fine cartilage joints in the fin rays can burst due to the high osmotic pressure. The fins fall off in large pieces and the fins are eventually infected with fungus and other bacterial infections especially when the fish becomes extremely weakened.
This is more of a case of prevention rather than actual treatment. Measure the conductivity between the water where the fish is and the water where it is to be transferred. The addition of mineral salt to the one with higher conductivity level will help minimize the chances of osmotic shock. Give the fish time to recover from the upheaval. Then, proceed to lowering the conductivity level to the desired level by doing small water changes over several hours.
Read more: http://www.tropicalfishkeeping.com/t...#ixzz1pgV78bnb