What kind of geraniums are you growing? I have a scented geranium that throws new white leaves when it has been in the sun so maybe you are exposing the plant to a little too much light. How long do you leave them under lights? I wouldnt worry about how much you are feeding them, but I dont have much experience with feeding fish emulsion. I feed mine a balanced 20 20 20 or 15 30 15, not organic, I'm afraid. There are varigated pelargoniums that will also throw new white leaves, so maybe you are growing some of those. Sorry I cant be of more help. Good luck.

Hummm Peat and vermiculite. Are they soggy and cold? Even baby plants like it warm and a bit dry. check your moisture level, vermiculite holds water. Back off on the foliar feeding they don't like their leaves wet.

I'm kind of having the same problem. I have my geraniums in pots, I have had difficulty growing things in the ground at my location. I've lived here for 20 years, and my previously GREEN thumb has turned BLACK! I'm trying my hand at container gardening again, and while I thought that geraniums were possibly one of the easiest plants to grow, (from previous experience years ago...) I'm having all kinds of problems. I think that overwatering is one of those problems, which I'm trying to rectify, think I will have to add more sand to my potting mixture, but I'm getting pure white leaves as well. Could it possibly be that my water source contains too much salt? Our community well is drilled into the "marine layer" of the Coast Range in California, geologically speaking, that is..., and the water is very hard, lots of minerals and salts in it, but I have no choice in that. Does anyone have any suggestions?

white leaf geranium--I have many outside (zonal)geraniums. They're all the same--except this one plant only is throwing off white leaves. The plant is
several years old, never done that before. ANd they never throw off white leaves
when growing....THey all get similar amounts of water.
An mystery but enjoying it.