My one Platy is looking very rough. Skinny, brown, not moving much, drooping rear end. I’m heartbroken and desperate for help!!

[GingyBreadman]

I have a 29 gallon tank that started with 3 ADF’s, after 2 months added 5 Blue Platy’s. That was about 2 months ago. The water levels are all fine, test them every 4 days or so. I just noticed after admittedly not checking on all of them to make sure they were all doing fine, since I always saw a good amount of movement. 3 days ago I noticed who I’m now calling “lil guy”. He is usually hiding or at the water surface alone, barely putting around. He eats, but not very much at all.

 

[Colin_T]

How long has it been skinny for?
It probably has intestinal worms but could also have an internal protozoan infection. I would try deworming them and see if it helps. You should feed the fish 3-5 times a day for the next month to help it regain some weight.
Do more water changes and gravel cleaning when feeding more often.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

The following link has information about treating fish for internal problems like worms.

What to do if your fish has Stringy White Poop.

Fish do a stringy white poop for several reasons. 1) Internal Bacterial Infections causes the fish to stop eating, swell up like a balloon, breath heavily at the surface or near a filter outlet, do stringy white poop, and die within 24-48 hours of showing these symptoms. This cannot normally be...

www.fishforums.net

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Before you treat the tank, do the following.
Wipe the inside of the glass down with a clean fish sponge. This removes the biofilm on the glass and the biofilm will contain lots of harmful bacteria, fungus, protozoans and various other microscopic life forms.

Do a 75% water change and gravel clean the substrate. The water change and gravel cleaning will reduce the number of disease organisms in the water and provide a cleaner environment for the fish to recover in. It also removes a lot of the gunk and this means any medication can work on treating the fish instead of being wasted killing the pathogens in the gunk.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.

Clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use the media. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens so any medication (if needed) will work more effectively on the fish.

Increase surface turbulence/ aeration to maximise the dissolved oxygen in the water.

 

[Lcc86]

Just to note if you do deworm the tank you will likely need to move your frogs out as some ingredients in deformer are toxic to amphibians depending on which brand you buy. If in doubt contact the manufacturer first. They would need to be removed for the entirety of the treatment plus a few weeks afterwards while you do water changes to dilute the meds out.