I have one of those too, on a good day mine is around that, usually it's over 1000ppm. I ran an airline outside to my skimmer to help a bit.My PH kept dropping and I grabbed one of these on Amazon. When the house CO2 gets up toward 800, the Tank PH starts dropping. Air out the house to get it down below 600 and the PH goes right back up to 8.10-8.30. Can really see the cause and effect.
BTW those are battery powered too, take it in the car on a road trip, we hit over 3000ppm with 3 kids, 2 adults, and a dog. Maybe that's why people get tired driving.