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Mollies eat plants: a cautionary tale


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Mollies eat plants: a cautionary tale.
I have a 75 gallon tank with assorted rainbows that used to be lush with various species of hygrophila, crypts, val, and some stem plants. It had a yucky hair algae problem due to nutrient imbalance, but I was manually removing it and it was a small price to pay for the great plant growth.

A couple months ago I was clearing out a molly breeding setup and needed to re-house some juveniles, so I plonked them in the rainbow tank to grow out. I had heard that mollies can be good for algae control, so I figured I'd see if they lived up to the hype. They mowed through the hair algae like a herd of goats! Cool! Now I had a gorgeous algae-free tank, my mollies had growout space, everybody wins, right?!?

Wrong. When the hair algae was gone, they started chomping on my plants! They decimated my hygros, ate my crypts down to the substrate, and even chewed on the tough vals! Even worse, it took me several weeks to realize what was happening. I spent those weeks mucking around with various ferts and trace minerals, thinking that maybe my plants had some kind of deficiency and that's why they were struggling. Finally I got some good advice from @Cory at Aquashella- he said that it was a learned behavior that started when they were eating the algae off the plant leaves and started seeing the plants as a food source.

I relocated the mollies to my shell-dweller tank where they're munching algae off the plastic plants and eating higher-protein food, and I'll likely move them among my other tanks as necessary. When they're big enough I'll sell them to local farmers for ponds and stock tanks since they like algae so much. I've salvaged or replaced most of the hygros and the crypts are re-growing, so I'm hopeful that the tank will be back to its previous glory soon.

So I learned a hard lesson - sharing in the hope that it saves other hobbyists the same heartache. 😊

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Thanks for sharing. Makes sense. Sometimes if fish find an _easier_ way to satisfy a craving, they’ll switch. I feed Omega One Kelp Flakes and Bug Bites Spirulina Flakes to certain fish in order to satisfy that plant-eating tendency. That worked well with some Buenos Aires tetras a couple years ago.

Edited by Fish Folk
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I have had similar experiences with platies picking at the roots of Amazon frogbit plants. In my case, even with supplementation of plant based foods they still do it. I guess once they get that habit it is very hard to get rid of. 

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