Water temp control in DWC. . .?

[aaonehundred]

I want to know how to control the temp of the water in a dwc??I don't have a temp meter right now(should be arriving in mail soon) and water is getting warm(is this bad)?.. . I don't know what to do? also what is the recommended temp?? thanks

 

[BUDISGUD]

recommended temp is 18c/24c,above or below isnt very beneficial at all

 

[aaonehundred]

Thanks BUD. .