Need opinions on a tricky soil grow problem (White Ice)

Hey,

I've read loads of threads on here, and concluded that I had probably overwatered my soil on day one, and suffered from oxygen deprivation effect ever since. I've got a few other strange symptoms now though, which I can't really work out.
-They still seem to be growing very slowly, though new growth is healthy and internodes are very tight. Maybe I'm just being too negative, but I'd expect wider growth by now? Maybe just a strain thing??
-Leaves that are more than a day old start to become brittle, and curl down (they do not droop down like over-watered ones do, it seems to be the brittleness that causes them do curl)
-The oldest leaves are now starting to show signs of a problem. Yellowing from the tips (veins and leaf) to brown. No drops yet.

I'm not a total newbie, (tho it's been a while) so I'm not frantic with worry. I don't think they're dying, but I want some other opinions in case there's something I'm missing.

My setup is CFL + LED (detail of the set up here on the LED thread: https://www.rollitup.org/led-other-lighting/513853-home-made-led-grow-lights.html)

In summary:
Seeds: White Label, White Ice (fem)
Soil: 50% good Wormcasting, 30% Perlite, 20% Peat-less organic compost.
Lights: about 25000 Lumens, 320W total power draw. (18/6 veg)
Temps: 25-19
Humid: 45-55
3 plants

The two biggest are 3 and a bit weeks old, and the youngest is about 1.5 weeks from breaking above ground. (youngest has only 20% Worm castings and a smaller pot - looks healthy so far, and no worries about overwatering, but the leaves are still curled down a lot)

I think my main issue is that the soil mix was bad. Too much WC, and not enough air. The mix was much finer and siltier than I expected. So I haven't been able to water these pots in 2 weeks!! Just the odd spray to try to loosen up the leaves..stop them being so crispy. I put extra holes in the pots, but just tried the cake test (pushed a balsa wood coffee stirrer into the pot, if it comes out clean its dry, if its dirty then the soil is still moist) and there's still moisture in there.
So, this suggests that I shouldn't water (to let the roots dry out and get more oxygen), and should just let things dry out over time...except, I've now started seeing some yellowing on the leaves. If there's a nute problem then I'm not sure how to fix it without doing more damage through overwatering.

Tapwater here is ph8.4, and I didn't realise it was so alkali until last week. So the initial waterlogging was done with this hard water. As a precaution I'm now adding vinegar to lower it to ph6.9ish, in case I'm looking at ph lock-out, but I'm still not sure I should be adding more water yet!

I'm pretty certain my babies are going to survive, as new growth is a good colour, but some other opinions would be welcomed. I can't get over just how short they are still. My plan was to switch to 12/12 in a week or two, but I'm not sure I should now.)

Here they are: (note: the one on the left seems to me to be a more sativa dominant pheno. I'm looking forward to seeing how this compare to the more obviously indica dom. pheno on the right. The one on the right is 4.5" tall, left one is barely 3"!!)

If it is an issue of lack of oxygen you could maybe try to do a mixture of water with hydrogen peroxide, although that might be premature I had used a mixture like that when I was growing some plants outside that ended up with what I think was root rot from too much water because of the rain, so peroxide it a thought but might wanna wait and see.

over-watering is the only issue i see. water by weight of pot. if roots are protruding on any of them, like that little guy, transplant to larger pot.