How long before I add more nutrients?

So I just built and started using this type of cloner. I added about 60 ml of clonex solution (which is an extremely low does as compared to what they recommend on the bottle) 4 days ago and dipped my clones in clone gel. I checked the ph yesterdaay and its right around 6.4. There are 13 clones. How can I tell when to give more solution or can i just let it go until my children are showing roots and are ready for transplant? Thanks all.

I'd say let them ride till you get roots that are 6-8" then hit them with some low dose
of veg nutes.