Every 3 days, I fill the buckets with more RO water, they drink about 3.5 gallons each every 3-4 days. This is no problem and very easy to do.
I don't add any new nutes when I add RO water, except for a small amount of bene bacteria to give it a recharge.
The problem comes every 2 weeks. I change the buckets to a clean one each 2 weeks, along with fresh nutes + water change. This has always been the easiest option as I have extra buckets, I can fill up an extra with clean water/nutes, make sure its as sterile and clean as possible, and just change the plant onto the new bucket. This works great until the plant is bigger than me.
I know your plant doesn't take up all the nutes in the bucket, just the H2O + what ever nutrients it needed during that time, meaning there's a really concentrated amount of nutes left in the bucket once you are low on water. I feel like even if I used a pump to pump out the rest of the water @ the bottom of the bucket every 2 weeks instead of just changing it to a sterilized bucket with fresh nutes/water, there would be chance to leave nutes in the bucket and burn my plants, or leave a contaminant in there long enough to take hold and give me problems.
The easiest option for me has always been to just clean a second bucket, put fresh nutes/H2O in it, and change the plant to the new bucket. This way I know EXACTLY whats in the bucket, and EXACTLY how long it's been since I've changed it last, so I can be 100% confident that nothing brewing in there.
Are you sure its safe to not clean your bucket for 2.5 months during flowering? That seems like asking for trouble with DWC and against everything I've ever been taught? Even before I used Bene's the bud booster and others would leave nasty residues, it seems like it would just build up a bunch of nastiness by the end of 2.5 months, I mean, how do you even flush in a dirty bucket? lol, especially a 2.5 month old residue-caked bucket?
Thank you for your input. So far my solution has just been to support the plants well and move the buckets right next to where u want the plant so you only have to move it 1/2 a foot, this way there's much less of a chance of messing things up.
I might get a pump, do 1 nute change with the pump and change the bucket every other nute changing (every month instead of 2 weeks), this seems like a fair compromise, do you agree?
EDIT: Also, what type of pump do people use for this? The fountain pumps require to be submerged and can't have a tube attached, so it stops suction once it is not under water completely (which leaves about 2.5" left in the bucket, which is no good at all lol). Also, I believe sticking a pump under a 3' cake of roots would present its own problems as I'd probably still have to lift the plant, meaning I might as well just change the bucket lol.
Would this work? Or is there a cheaper option.
http://www.harborfreight.com/12-volt-marine-utility-pump-9576.html
My goal would be to stick one tube in the bucket I want to empty, and another tube in a empty bucket or even out my damn window lol, turn her on and let her go, is this the answer?