Hi folks,
This is my first recirculating attempt. Individual buckets are easy - drain it all. But with all the hoses and fittings, I have about a 10% hold-over by volume.
Dry fill is 66L
Pump-out and refill to same level is 60L
I plan on running sterile.
Is 90% change-over decent enough if I shock it at every change?
Was gonna scrog the 4 plants so ideally no touching of buckets unless something goes terribly wrong…
I dont see any huge problem with that, but…
How big a potential problem it is, has more to do with the nute balance than with any bio hazard between changes.
If you are feeding at the correct EC/PPM level, and the PH is staying in range between changes, then it would be pretty much a zero issue.
On the other hand, if you are feeding at too hi or low an EC/PPM, and/or the PH goes out of range, then the nutes can get seriously out of balance between rez changes. That means that 10% left over will be low on some nutrients, and hi on others. That imbalance can add up over several rez changes.
Still, 10% hold over probably wont get serious unless you’re really screwing other things up 
If it bothers you, you can always do an extra rinse when you change the rez. Drain as usual, then refill with plain water and drain again right away. Then top off as normal with your mixed, PH’ed nutes. That will get you from 10% down to 1% or so.
Do you monitor EC/PPM and PH between rez changes? If not, then you really should. Its the only way to be sure you’re feeding at the correct levels.
Thanks @anon32470837,
In the past, in single buckets, I have not monitored, but changed and adjusted weekly.
This time around, with a control bucket and decent metering equipment, I plan on doing so.
I went down the rabbit hole and saw that some people don’t change the solution at all during their grow. A little skeptical, but that did reinforce what you are saying - monitor what’s going on and adjust accordingly. I think I’ll try it as is then; it would be a serious task to make it so that all of it gets changed.
Thanks again
HH
Shop vac it. That’s what I do with my system
@SquirtleSquad, this is brilliant, i can’t believe I didnt think of it. Here I was thinking up all sorts of crazy contraptions, when good old Ridgid is already in the basement, anxious to suck, working as a surface to rest my drink most of the time. Thanks!
