How to care for platy fish in a 72L tank and prevent health issues?

If the tank was not properly cycled before she went in, the water qualityu may be affecting her. Check the water parameters first. Temperature should range bewteen 68 F and 78.8 F (20C to 26C). Using a home test kit, ammonia and nitrites should read 0 ppm. Nitrates should be 40 ppm or less. Platys do best in a pH of 7 to 8.3. Adjust parameters as needed and see if it makes a difference in her behavior. Offer a variety of appropriate pelleted and flaked food as well as freeze dried to see if she has a preference. Platys are livebearers with a gestation of around 28 days. She will become noticeably bigger as her date approaches. If she is pregenant and has fry, you will need to separate her or give the fry plenty of cover in the tank. If not, she will eat them. The stress of a new tank and water may also be a factor. Hopefully, with some adjustments and different foods, she will perk up.

Chances are if your female platy was kept in an aquarium with male platys the likelihood of her being pregnant is very high. The general rule for keeping both male & female live-bearers in the same tank is a ratio of 2-4 females per male. The reason for this (which you seem to be experiencing) is that the male will become very persistent and chase the females around. Keeping more than 1 female will help alleviate some stress in your aquarium. Both the male and female platy will try to eat the young fry once they are born so you may want to confine the female to a “floating nursery” until they are born. Once the fry are born, remove the female and place her back in the aquarium. From there you can keep the fry in nursery (or move them to another aquarium) until they are large enough not to be eaten.

It depends on how big the tank is as well as the type of filter in use. Smaller tanks and more heavily stocked tanks will require more frequent water changes, about 20% every week or two. Check the chemistry (ammonia, nitrites, nitrates, pH) regularly. This will give you a better idea of when to perform tank maintenance. Tetras and platys are schooling fish and ideally, do better in groups of at least 5 or six.

In general these fish can all be housed together safely. The one thing to keep in mind is the amount of space needed per fish to maintain a safe and healthy environment. Each 1in of fish needs 1 gallon of water. So in a 20 gallon tan you can have 20 inches of fish. The Pleco is the only one I have concerns with as some varieties can grow quite large. Check with your local pet shop as to what needs best suit this type of fish or what type of fish suit your tank best.

It doesn't look like Ich in the images provided. Ich will appear as multiple white dots the size of salt grains on the fish. The fish will "flash" or dart about the tank and rub on objects due to itching. The fish may have an infection or the loss of scales may be due to trauma from other fish. Consider separating the affected fish into a separate tank to recover. If this is not possible, maintain pristine water quality in the main tank and consider a broad spectrum antibiotic. You can find one in the aquarium section of the local Petco. Follow label directions carefully and remove the carbon filter insert during treatment if indicated. You are likely at the maximum number of fish in the tank. As they grow, they shouldn't get bigger than 2 - 2.5 inches, and reach adulthood you may need a larger tank or you may need to separate them.

Keep her separate to prevent further damage. Maintain water quality via frequent water changes. Use only aged or conditioned water that is temperature matched to prevent stress or shock. Platys do best around 78F. Dissolve 1 teaspoon of plain aquarium salt (NOT table salt) per gallon of water in a cup of tank water and gently pour it into the tank. This will reduce stress, treat minor infection and aid in recovery. You can also add StressCoat or StressZyme. Treat with salt for 10-14 days then reassess fin condition. The fin should grow back eventually, then you can return her to the main tank.

Some platys will have black spots on their bodies. This is normal and no cause for concern. Monitor for lethargy, decreased appetite, rubbing on objects or "flashing" (darting about the tank). Check water quality and chemistry. Make sure ammonia and nitrite levels are at 0 ppm (parts per million). Nitrates should be less than 40 ppm.