Ok I have had countless ph issues because I mixed the soil wrong because of a meter I did not know was broke...(Rookie Mistake) Anyways I have flushed several times because of reoccurring lockout issues and I was thinking of mixing lime with water at the end of the flush in a attempt to neutralize the aluminum sulfate even a little bit.
I did this one my first grow (link is in my signature) you can check it out to see what i sued. I was having issues with my soil - i think it had a buffer in it to keep the ph low. I ended up having to use a ton of it but it saved my grow - I would suggest using a quick acting lime, mine dissolved in water no problem. If you use something similar to what i used then it is 1 tablespoon per gallon of water to start with. My PH issue was so bad I ended up using about half the bag on my grow but mine was an extreme case.