Lonewolf,
Did you cut off those small pups from the mother plant or was that the way they were given you? I would be afraid they would not have enough rhizome on them to catch on. Too small to continue to grow and stop or reverse to juvenile stage. That is very risky to do. But all said I do like the collection and in the fish tank, they do have the best environment to grow from. I have mine in a 55 gal. fish tank but I have them potted up in their own pots. As small as they could fit. Seems they like it better.
Showing below is my set-up. Highlighted is my special 'Streaker' with it's new pups. I hope they stay this way. So far so good. I will not cut off from mother plant but I will cut the largest pup from them. The original mother plant is the one on the top potted.

The pups were taken off of the parents. I've done this in the past with allot of success. I won't detach if there isn't much rhizome or roots.

I need to bring in my other 'Streaker' plants from outside. The yellow one I got is still out there in serious need of a good watering. I do got a 135 gallon aquarium I should be able to use later on down the road once I sell off most of my fish. I actually got 2 of these aquariums but need to sell off one of them. Room isn't big enough for both of them. I can setup a 5 gallon for my 'Streaker' plants though so I can bring them inside.

Does your aquarium have a lid on it or is it opened on top? Mine is partially open.

Mine is mostly open. Just the 4 ft. shop light. Using two T-8 bulbs (daylite). Light is on about 15 hours a day and the pups are growing fast in this hi light condition. Temp is around 70 degrees. I was thinking of having a small candle in a jar under the tank. About 2 ft. below to increase the heat. Of course lite only while I'm there.
Stush