My answer is the same I answered the squid, I live in a small town in eastern europe, you can't find anything useful here, I have to order everything online, it takes at least 2 weeks to have anything to transplant in with the ordering and shipping etc. But as a last resort if things keep degenerating I will get some regular soil that's a good idea, but I won' find any proper nutrients here. So far seems the flushing and lowering the lights has an effect, still to early to see improvements, but it's not getting any worse either. When the yellowing appeared it was sudden and quick now it seems to have at least slowed if not stop I hope.