Surge of growth after 5th week of flower.

Just wondering if anyone sees this?

During flower, I do a flush with each rez change. When the rez has enough solution to run just one more cycle I add a couple of gallons of RO @ 129 ppm which bring the rez ppm to around 350, pH and flush.
After the 5th week, when I add Liquid KoolBloom, I do a major flush. Three to 5 gallon added to the last cycle of the rez only adding Drip Clean, and run one minute cycle about 15 minutes apart till rez is empty. Then I refill the rez with my regular nute solution. I get 6 to 7 days per rez fill.

What I have noticed is a burst of growth right after the flush that last until I harvest.

Anyone have any thoughts on this?

As a soil grower, I recognize this. Soil dries, roots grow below soil, growth above soil stalls. Saturate soil when its dry and growth above soil explodes until the medium dries and roots expand again. Rinse and repeat.

Coild be a buildup of salts locking out good nutes. After flushing they take in more nutes.

That is true. That is why I do a mini flush with every or every other rez change.