I personaly never water or flush with my 7.8 wellwater. 1/4 tsp phDown per gallon of water put's me at 6.8. To that, I add the nutrients. Too acidic or too alkaline can damage sensitive roots.

Consistent watering is more difficult with every jump in pot size.

When watering the larger containers, I find it especially important to use a slow-trickle type of watering. I add a quart, wait a minute. Add a quart, wait a minute. Keep doing this, till you get a slow trickle of runoff. I do this with every watering and every feeding.

With larger containers, you can get dry spots in the soil. Since I flush every month, I avoid that problem. (mostly, lol) Sometimes I'll have to gently 'squeeze' the pot after watering to destroy the 'rain channel' effect, where the water follows a set path to the botom of your drainage tray instead of absorbing into the medium. Don't crush your roots though.

Everything else looks ok to me. Old leaves are old news. How's the new growth looking?