I think Seachem product (7.0) should be used when pH is arounf 7 to keep it staablized at 7.0 Again pH will swing as
buffer exhaust w/ time.
If KH is high, it means you will have hard time lowering pH. So why add more buffer?
How about this?
Take some tank water out and put peat moss w/ little aeration. Test pH before and 24 hr after to see if it will help you reduce buffering capacity.
If the pH dropped myabe you weant to treat tap water w/ Peat before
water change Only when necessary (trying to lower KH and pH). Will give you little brownish tint which can go away w/ time as long as peat is not used all the time.
Its been so long (25 yrs?), cant remember exactly the results of many experiments I ran.
Hope this helped a bit.