I used to enjoy fresh air into the fish room too via the portable AC unit. Now that I switched to a minisplit system, I lost the benefits of the constant fresh air but fortunately the room still breathes well and my pH only dropped just a hair from before when I had fresh air from the portable AC.It is a wonder drug along with outside air for the skimmer! I get about the same pH bump that FarmerTy does. In the summer with the house closed up, I used to bottom out at 7.7-7.8. Now I bottom out at ~8.0.