Citric acid

I dont think theres any need to add citric acids to the soil, flush is about running high volumes of water through medium to remove salt buildup, not basically sterilising your substrate which could ultimately harm the plant right at thebfinal stages - its all about osmosis with plants, find the balance.

0.5g citric acid per 1gal water for flushing, probably with alot of runoff. But I wouldn't do it if you are not flushing with runoff. Plain water ppm below 100 flushing should be enough. I found that using Florakleen a.k.a FlashClean during the initial flush help break down the minerals/salts much better. I don't flush with runoff due to the fact I don't have a place for the runoff to go. I feed using FlashClean when I had buildup & nutrient burn... and it helped alot for me. Probably 30% more efficient than just feeding plain water. Took 2-3days for the plant to show differences using FlashClean compared to 5+ days just feeding plain water.

Personally, I don't think this is a good idea, you may burn the plant and cause much damage, besides, I can't see how this would achieve anything. Just use plain water for the flush, nothing else. Flushing is not about washing/leaching the bejeezus out of the soil, but about removing mineral salts from any fertilizers used, out of the plants cells, and this is best achieved with plain water. Using just plain water for the last 5-15 days before harvest and using what you would normally give as an irrigation amount is all that is needed. There is no need to drown your plants, which can lead to bud rot and other problems, even when drying. Hope this helps, Organoman.