Love the immersed tank Bro!
That's some awesome looking stuff!
Speaking for myself, I don't believe in buffering....either the fish live or they don't. They should be able to tolerate those conditions, but if you go back to changing the water on occasion, it may allow them a little time to adjust to less frequent water changes. Considering catfish are genetically able to swim around in all God-awful, low pH, poorly oxygenated, murky filthy conditions, the key seems to be conditioning them slowly to get used to those types of conditions. You may be going a bit fast. That's how I did it.....I gave up buffers over a decade ago because it never really helped me in the long run and too difficult to manage on a consistent basis.
Tank looks good....could use some Ludwigia sp. 'Red' though.