Check out some vids on you tube.
You are looking for the drop checker to be nice lime green (a few shades off yellow) at lights on. Eg. For my 100L tank I put it on 3 hours before lights, but loads of surface agitation.
have a look at Denis wong on YouTube. Brilliant videos. He explains a lot.
Also his website https://www.advancedplantedtank.com/
I can’t recall the the size of your tank, but start with 1 bubble per hour and move up. Bubbles don’t mean anything though really. Different regs have different size bubbles and larger tanks need a stream.
Do you have fish in the tank?
Without fish, adjusting the C02 levels, is a lot easier than with fish!
Anyway the best way to understand how it effects the water is by doing a PH profile.
You will be useing quite a lot in a 240l tank, my 200l used an uncountable number of BPS. However that depends on your lighting and distribution methods.
Well it is easy enough but it takes all day!
Basically you take a PH reading every hour starting just before your gas comes on and every hour until your lights go off.
There is a target figure of a one point PH drop by the time your lights come on and a stable PH until lights out.
This sometimes proves impossible in which case you would need to look at flow or distribution.
Most folk use a cheap PH pen unless you can justify an expensive pen of course...
Yes correct, this is a popular method for estimating 30ppm of disolved C02 in the water column.
It is not a fail safe method due to a few factors like the accuracy of the pen, whether or not you have hard water or other chemical in the water that might effect the readings but.... it is a very good method to show how affectively your system is Woking.
As a general rule the gas is switched on two hours before lights on and switched off one hour before lights off.
A good starting point for your PH profile would be to record your tap water PH and your tank water PH after it has been standing in a glass for 24 hours.
Once you have made your graph it will be very informative and will make it easy for us to advise thereafter.
It is a good idea to keep an eye on you drop checker colour as you record the graph as that will always be your long term indicator.