Yes he is getting a build up
you have won the prize
good answer
mix bennies into your mix next time, the right bacteria`s brake down calcium phosphate
This can be a problem with people using tap water as there is a lot of cal in most tap water and then they put chlorine and such in the tap water this kills the soil bacteria`s and mean a cal/phosphate lock is possible
tnc sell bactor 13 or something like that
but there`s 100`s of such products for any way you choose to grow
I use a water butt my water bubbles away for a few days to a few weeks with some bennies and treatments in there to help make it better for the plants, ph`d of course
I try to just run 6 to 8 week strains
I don`t re-use my coco it go`s to my outside plants, due to bug issues but if I did I would bucket it up and add some fresh bennies to it let it brew for a week or 2 before re--using it
also I like a perlite coco mix for sure easier to work with, plus I put pure perlite in the bottom of the pot (stops bugs, rot and makes transplanting easier) and I top dress with perlite too (stops bugs getting into the coco/rootball)