Sick Black Molly


I have a Black Molly that seems to have a recurring problem with being sick. About a month and a half ago I had to treat my whole tank for fungus (the cotton like stuff). I used the API Fungus cure. A week after the tank was cured this same black molly got the fungus again, so I treated the tank with the fungus cure again for fear that the other fish would get sick. I also treated the sick molly with salt water dips (1 tsp. aquarium salt and 1 gallon of water for 30 mins) every second day until the fungus was gone. The treatment seemed to work as the fish has been fine for about two and a half weeks post-treatment.

Tonight I noticed that the same molly has one white spot on him again that I suspect is fungus as well as these thicker string type things coming out of his right gill (see picture below). I don't know what to do with this guy and I'm worried about the other fish in my tank but I don't know that its a good idea to treat the whole tank again for just one fish.

Tank specs:
10 gallons- filter, heater
Fish- 2 black , 1 red mickey mouse platy, 3 guppies

Water parameters:
pH 7.6
Ammonia 0 ppm
Nitrates 0 ppm
Nitrites 0 ppm
20% water changes weekly with a gravel vacuum for debris (I try and not let the bottom get too gross with fish waste and I feed them two smaller feedings in a day to minimize food wastage sinking to the bottom)

I need help urgently please as I am leaving tomorrow evening for the weekend. Any info helps!


The photo you posted isn’t working for me, but at a guess maybe anchor worms could be the string thing you describe hanging from the gills?

I would definitely quarantine off that one molly and try to get to the bottom of what’s making it ill, sounds like it may have some more severe underlying cause that makes it very susceptible to illness.
Sorry I can’t really be more help

Crafty Cichlid

stringy gills def sounds like some sort of worm.

What's your temperature in the tank?

Try creeping the temperature up to ~80F to ward off fungi. Medicate according to instructions on medicated box.

Image isn't working for me either.

How old is the fish, and are your certain it's male?
  • Thread Starter


Just posted the photo as a single reply so hopefully that works! I keep the tank around 78*F so I'll try raising it a few degrees. I got the fish around the beginning of December so not all that long ago and the store tank was labeled as them being male, I bought both of my black mollies as a pair and I haven't had a problem with the other one :/

devin s.

If he continues to get sick and infect your tank, you may want to consider rehoming him.
  • Thread Starter


I don't really wanna give up on the little guy :/ anyone have some treatment ideas?

Crafty Cichlid

Quick and dirty of sexing mollies, platys, swordtails, guppies, etc. Think Kindergarten Cop: "boys have a [gonopodium], and girls have a [well, normal looking analfin]." Males are often smaller too, because they're not full of a million billion babies, and never will be.

I agree with devin, sometimes it's time to say goodbye. If you're not ready, no pressure, there are ways to save the tank and the fish.

More questions though.

When was your last weekly water change? - - - If you haven't done it this week yet, don't.
  • Change your filter pack instead. If it's a sponge filter, fill a bucket or something with just enough water to fully submerge it, treat the water (dechlorinate), then swish and squeeze the sponge around until you're pretty sure most of the gunk is in the water and the filter can't be more clean. If it's a charcoal/activated carbon filter, discard and put a new one in.
  • Avoid changing your filter and your water within three days of each other. Lots of good bacteria live on the filter, and in the gravel. Clean both at the same time, and the water can get super toxic, super fast, and then your fish get sick.
  • Small tanks can be harder to keep, because if the bacteria in one part of the tank gets off balance, the rest of the tank can't compensate. In tanks of any size it isn't a bad idea to over-filter. In a 10 gallon tank, I'd run a filter rated for 20. In a 20-30, a filter rated for 50 gallon tanks. In my 30, I'm running one rated for up a 100 gallon tank, I'm also slightly overcrowded - long story for totally different types of fishes.
    • Don't kill a fly with a sledgehammer though, a filter for a 50 gallon tank isn't going to benefit a 10 gallon tank .
If you did just change your water withing the last 24ish hours, do it again - sometimes a 50% change isn't a bad idea, just always remember to dechlorinate. After 3-5 days, change your filter. You can also swish the filter pack in the water you're going to discard - you'll keep the bacteria, but get rid of excess gunk.

Salt can help too, API makes a freshwater aquarium salt (there's probably an advertisement for it below!), and has instructions for how much to use. Mollies come from estuaries near the end of the MississippI river. Water there can be 0% salty to 150% the salinity of standard seawater, and the fish transition easily. I've read about saltwater enthusiasts using them to cycle marine tanks. Your other fish will tolerate it well, and the guppies especially might go play in it/nip at it, while it dissolves.

Keep asking questions!
  • Thread Starter


So based on the photo above I have two female mollies ;D I did the weekly water change yesterday actually and I thought you weren't supposed to change the filter? I ran into a bit of water quality issues doing that in the beginning of my tank and just recently put a sponge in there instead of the carbon filters that came with my tank set-up. I always dechlorinate the tap water before usage.

I actually have some API aquarium salt but have never used it other than the salt baths when the molly was sick the last time. How much should I put in the tank? The box says 1 rounded table spoon per 5 gallons so that would mean two of those for my tank. Is this too much for the other fish?

Also, would treating the tank with Jungle Lifeguard help? I'm really concerned about the possible worms and I'm not certain that it will just resolve on its own?


No, don’t change the filter. It’s where all of your beneficial bacteria live. If you change it, the tank will need to be cycled again.

Crafty Cichlid

Sponge filters, at most only need a swish and a squeeze in treated water. My LFS did that about once a month with his. Think of it as part of your gravel, need to get some waste out of it here and there, but doesn't need replacing.

I've never had parasitic worms, so I couldn't say.

I just toss in a handful, but measuring out to the box's specs won't hurt your fish.

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