My new toy....need some help

[support@proline]

1-yes the purpose of the valve is to regulate floew through reactor
2-CO2 drops the ph in the reactor &breaks down the aragonite media to provide you with ca+2 & carbonate for alk maintenance.
you have to have a balance between the effluent rate ,amount of co2 you inject & your consumption.
You don't want to have the valve too open ,that way you are wasting alot of CO2 & potentialy droping the tank ph .of course that all depends to what is your consumption levels.
The reactor can handle pressure ,as long as water is still exiting it .I have never seen any brand of reactor that had a problem with the extra pressure.
3- yes you fill both reactors with media ,you can also use some Magnesium media in conjuction to the arogonite to help maintaining higher levels of Mg without having to dose any liquid additives.
4-You have to test the effluent for KH & your tank water for KH & CA to fine tune the reactor to your tank needs.
I hope this answers your questions