FloraDuo DWC, used a ton of A (GROW) and need to switch to Flower, plz advise

So if my subject didn't explain enough, my ppm levels in the DWC buckets are in the area of 800-1,000 ppm (AK-48, so very heavy feeders), and I used the Strong Grow Blend of the FloraDuo formula (75% FloraDuo A). I have no ability to drain as it's in a ScrOG, and now I need to switch them to flowering ASAP, but I used the Heavy Growth formula not realizing how quickly my clones would grow, I guess because they were sitting around in rockwool waiting their turn for so long.
Now I'm in risk of seriously overgrowing the screen, considering the stretchability of AK-47, and I just want to switch off to flowering ASAP. I would deeply appreciate if someone would advise how to proceed, because just to get to the MILD Bloom Blend I would have to push ppm levels up to c. 1,700, which is obviously way too much.

If your growing in 5 gallon buckets then drill a hole in the top and put a hose in and attach it to a basement pump from menards, around $60, and then put gorilla tape on the hole to keep light out. You need to plan on having to move your plants during the grow cycle or have the water flushed out. What kind of container are you using to keep the plants in?

About six gallon Rubbermaid buckets. It's not very modular, since it's a ScrOG, didn't plan on having to flush as with FloraDuo I can basically work it out on my own when refilling the buckets. I think that's basically what I'll have to do, is siphon or pump the actual water out.