I had a fourth gen UJSM, that took forever to finish and got down to SG 1.05 at best. Using a 30ltr bucket fermenter, I added back about 4 ltrs and the ph was down to about 3. I wasn't sure I if I should keep adding less backset, so I used about 2 table spoons of calcium carbonate for the 30 ltrs, and it came back up to 5.4 or so, so I pushed ahead with the 5th gen.
The ferment still took longer than the first three gens (about three weeks), but went through to 0.990, so I can't complain.
This lot has been on dominoes for about six weeks, and i am not able to detect any ill effects to the taste. I did the same with a BWKO, and haven't had the chance to check this, although I am expecting the same result.
Very happy with this approach. :handgestures-thumbupleft:
Edit: I did add small amounts and test as I went until it got to the 2 table spoons worth.