Yes, plants do use some O2 at night, but if they are receiving proper light and nutrients, they will produce more than enough O2 during your photo period to take them, and a substantial fish load, through the night with no issues. An airstone is not the right way to approach that issue in IME and will not help with plant growth. It can help if your tank is out of balance and your fish are gasping at the top in the morning though.
Adding an airstone during the night will also help drive your CO2 down, potentially increasing the difficulty of early photo period CO2 rebound with your already overstressed DIY CO2 system. Inconsistent CO2 levels are a leading cause of algae.
I see you are also on our local AZ board. I highly suggest you come out to a meeting or two. There are a lot of great folks here locally who would be happy to help you sort all of this out (me included)
Good luck - This can get addicting!