Tap water pH suddenly way higher than tank pH

[Novembersdoom6]

Hello everyone! I had a quick question I was wondering if anyone might be able to give a bit of advice on. 

My tank has substrate which buffers my pH down to about 7.0, which is ideal. My fish and plants seem to like it. My tap water used to be about 7.2, which was close enough that I didn't worry too much about the difference when doing small water changes. But now my tap water pH has jumped up to about 8.6. That's extremely high, too high to do WC's now. Tap water GH and KH are also higher than the tank water. Realistically it would be difficult to try to pull all the substrate out and put in new substrate and try to slowly have the fish adapt to a pH of 8.6, being so much higher and also even on the high end of what South American fish can adapt to.  It just seems like it would stress the fish and plants out too much trying to make them adapt to the huge difference. The pH has been this way a couple months so it doesn't seem it was just a temporary thing.

I'm thinking it would be easier to just pre-mix my water and use a product like pH Down  to lower my tap water's pH to about 7.0, and also possibly make some GH and KH adjustments. Just trying to match everything as closely as possible. Would that be safe and stable long-term, or would using an acidifying product like that to pre-mix water cause problems? Would it possibly lead to instability and swings in the long term? I need to provide stability, but when my tap water differs so much from my tank water, I'm not really sure how to go about providing that stability and safety. Would RO water be the only safe or recommended option?

Thanks and have a great day!

Edited December 21, 2020 by Novembersdoom6
Typographical errors

[AdamTill]

First, I’d run an airstone in a bucket of tap water for 24 hrs to see if anything changes. Sometimes chems are added to protect piping that are not stable long term.

Next, try to see if the changes are long term changes. If they are, I’d consider adapting the fish slowly to the new tap water. I’ve managed RO and remineralizing long term and it’s a LOT of work on weeks where life is getting crazy.

If it helps, I’m breeding otos at 8+ with no issue, so most species can adapt. Plants especially.

Edited December 21, 2020 by AdamTill