Well this answers a few things I see.
First off STOP any flushing! You did not have an overage or nutrient toxicity of any kind.....Now you do have an S and Ir def.!
See the new growth being thin and yellow? Sulfur and Iron def.....
What are you feeding with - list everything that goes in!
Get some Age Old Kelp extract and foliar feed some at 2tsp per gallon. Cover spray both top and bottom of leaves. (Iron and Sulfur)
OR
A good Ca/Mg product like G&H CALi MAGic......This particular one will help control pH swings and slowly add back the Iron and the Sulfur...
Soil self pH's and you really don't "need" to attempt to adjust it.
Sometimes you may add some dolomite lime to the soil and mix it in before planting. - Depending on the soil mix used.
If you "push" your plants with a synthetic. You should do a watering with a simple bio tea at least once a week. That adds back active living bio's to the soil aiding in many ways - YES, even with synthetic use...
If you feel you must pH your in-going. pH to 6.5 in veg and 6.7 in bloom and forget about "soil" pH!