If they have weight then make sure they dry out quite a bit before you water them again. Overwatering may be the problem here causing aneroebic conditions. If you have been letting the pots dry out between waterings then consider getting rid of the silica and going with a general purpose...
Could be an iron deficiency. But I would ignore that for now. Do you put the pot back in it's saucer when you are watering? If you don't I would do that and water from the bottom until it stops drinking with whatever you normally feed with. Put a few inches of whatever that is in the saucer, go...
If there is one tip that I think applies here it is not to have an end date in mind. At the end of August wait another week or two. Most people harvest too early in my opinion.
Wait until all white hairs have browned and receded, wait a further two weeks then harvest I think I have heard. Might be a good starting point until you find your preference. Err on the side of waiting longer if anything.