Oof 6 gallons is a lot. I use 1 gallon which is 3.7L. I needed to automate because it got bone dry which kills my plants every time. Just my experience and many others and people will say its due to that.
It became obvious to me later on, I only let them lose some water its retaining and feed again 3 hrs later. Still wet to the touch but absorbs water for the first half of the feeding cycle.
Then it puddles up and finishes. Flushed out old solution. Replaced with solution high in dissolved oxygen which is like nitrous oxide to racers but in growing.
Yea 1.8ec since sprout just to add that they can handle alot. Manufactures recommend super low ec that is equal to my tap water. Just a pain I dont bother with also for clones.
I have one reservoir feeding all so its nice to let it feed of my main reservoir instead of itsown. Idk what else youre adding but I only use maxibloom and poolshock to keep sterile, reservoir can rot.
Anything else isnt needed. People will add silica and other minimal things, I wouldnt worry about it now if ever. Idk what you mean struggle to runoff, its great for the plant to feed to good runoff regardless pot size.
Learning to check runoff ec can help fix problems half the time. My mini clones are done and can see where I fixed an issue and finished clean.
My bigger plants have a unknown issue popping up of colas just straight dying no one knows why. I overfeed but my clones look like shit when I dont. Meh everyone has their struggles.