[Nevermore]

In my experience, it's a nutrient balance issue, just like everything else. I've seen it occur with either too much fertilizing or too little. It's easy enough to fix and not the unstoppable force some people say it is.

You say it's "easy enough to fix", maybe you can elaborate.

 

[Nevermore]

It was suggested to me to up my PO4 from 1 ppm to 2 or 3 ppm. All that did was increase the issue. I read an article by Tom Barr who was talking about a balance of PO4 and CO2. The higher CO2 concentrations needed less PO4. blah...blah...blah.

Well, increasing the PO4 is usually recommended for GSA, not GDA.

I'm in the "c" camp btw.

 

[Nevermore]

My GDA is on the plants as well as the glass. It makes it much more of a nuisance. I'm decreasing the photoperiod to see if I can get rid of it.