Getting ramshorns to grow BIG

Has anyone had any success with growing large, healthy ramshorn snails? Mine never get much bigger than a BB pellet. I'm guessing they just die before they can grow larger? I know these things' shells can grow as large as a nickel.

I know that living in a tank with fish can be hard on them, but they don't grow very large in my planted shrimp/hillstream loach tank either. Nothing in there should be able to kill or even hurt them.
The pH is around 7.5-8.3. The terra cotta decor in there seems to keep the pH from dipping low enough to start damaging their shells.
The water's pristine thanks to the abundance of plants. Clean enough for a thriving shrimp population, so I don't think the water's toxic. I also haven't used any worm killing pesticide in there that would affect the snails.

I can only guess it's due to a lack of food? I don't feed this tank a ton since it's mostly filled with shrimp. The largest ramshorns I've seen were always from outdoor ponds, where they presumably munch on all the biofilm that direct sunlight can grow. Do they need a daily feeding to grow larger?

 

Cooler water and not too much food. The idea is the slower they grow, the longer they live and the thicker/healthier their shell will be. The ones I have in unheated, unfiltered but lightly planted and lightly fed 1gal pickle jars are significantly larger and healthier than the ones in my planted, heated, and filtered fish tanks. You just have to remember to change some of the water a couple times a month. Dime-penny sized is about as big as mine get, a few have gotten about as big as a nickel though.

 

I have ramshorns but I also have dwarf ramshorns that only get about 2-3 mm. Could you have dwarfes?

 

My ramshorns in the QT were growing with thin shells. Cooler temp, high pH, food controlled, sponge filter. I added a sepia, since then the shells get thicker and more uniform in color, and they are growing.

 

I too have noticed my Ramshorns get larger with less food. When they get more food they produce a lot more snails but they don't get as large. Maybe the latter results in a higher snail to food ratio? My cold water tank snails also get larger with older looking shells than the warm tanks.

 

the ones i have in the outside patio pond get to nickel size with lots of algae to eat and very warm temps 90-95'F.

the ones inside only get about dime size with minimal food and temp around 77'F.

 

The ones in with my frogs get to about 1/2". The ones in the other tanks get about half as big. I think the frogs eat enough babies that there is food for the bigger ones to grow.