Rambo:
Don't try to move a plant until you harvest it; a pump is the answer to how to change nutrients on a big plant. Install a
Bottom Draw Pump in the bottom of your reservoir before planting and just pump the old nutes out a hose - easy peasy. My current grow space pumps or gravity drains my waste water out into my flower garden outside no waste and gorgeous flowers. No lifting - I have a bad back.
Don't try to mix your nutrients in the reservoir with your plants roots in it. I have a 35 gallon top off tank on a stand outside of the grow room. Water/nutes in this tank are aerated at all times. It is plumbed to carbon filtered water coming in. Outgoing it is connected to my reservoirs and the drain with valves to direct the flow. My city water is pretty good at ~ 125 PPMs. First I fill the top off tank with filtered water and aerate overnight this dissipates the remaining chlorine added by the city and releases some of the calcium carbonate raising the PH. Then normally you add parts A - B to the water and adjust the PH using PH up or down as needed then add the rest of the nutrient components. Test the PH again. Follow the manufacturer's mixing instructions to the letter. Next I do the res change by pumping it out and refilling it from the top off tank. It takes me about 20 minutes so the roots are never in danger of drying out or stressing the plant. I have my system dialed in so that there is about 25% (~9 gallons) left in the top off tank after the reservoirs are refilled. Then I simply refill the top off tank with filtered water now I have a 25% strength (of the solution that went to the res) nutrient solution to keep the reservoirs topped off during the week. I know it sounds complicated but once you do it it becomes simple.
I have run Botanicare HydroGuard in reservoir temperatures as high as 87°F - 30.55°C without any root problems! Daytime temperatures in my tent reached 95°F on many days. I run 2 high volume air pumps (redundant in case one fails) when using DWC. I live in the San Joaquin Valley of California and we average 63 days of 100°F + every summer. Now I know that lots of people will tell you your res cannot hold enough oxygen at that high temperature - Hog Wash I have 2.5 pounds of high quality bud that says otherwise.
The high reservoir temperatures I get here in the summertime are the reason I am experimenting with a rockwool block grow right now. It pretty much negates the oxygen question. Will it improve my yield? Follow the grow in my signature and we will find out.
I don't know how to stress the importance of maintaining your water level in the reservoir at a constant 1/2" to 1/4" below the net pot is to the final result. USE A TOP O
TANK with a float valve in your res. Be sure to position the valve so that roots will not interfere with its operation.
I don't know if you can take an auto to 300g but this is 2 Fast Bud Green Crack Auto plants that yielded 370g cured:
