I got real busy and didn't dose ferts for a week. The slimy brown diatom-like growth went away. I dosed again, just for a day or two, the next week. Stopped dosing. It went away.
Plantbrain (Tom Barr) said that in low light tanks less nutrients are absorbed by the plants. Perhaps this is why you no longer need ferts. Which is good when you are busy.
Maybe the neons I had were just extra sensitive or something?
I haven't been able to keep neon's alive in my tank. I read that others were having a problem with them, for they are not as hardy as they used to be.