Hi wordy,
I have and use a D-D regulator set. You'll have no need for rowaphos if its a planted tank (its actually detrimental to use it on planted tanks anyhow) but it is a usefull product in non planted tanks.
Firstly how many dials did the set come with as I know they sell two different sets although the componant parts are the same. Has it got a solenoid control valve? and did it include a co2 diffuser?
Not long ago I was involved with a similar thread on these regulators so it may be worth reading this:-
http://ukaps.org/forum/viewtopic.php?f=37&t=6208
I can't remember exactly whats in the above thread so will quickly run through setting up this reg for use. Assuming all the conections are made and good (check with a washing up liquid solution) and your diffuser is fitted and ready to go.
Set the needle valve aproximatly halfway between fully closed and fully open then turn on your co2 and set the dial pressure to about 1.5 bar. Its actually usefull if you pick a line on the dial and set the needle bang onto this line it doesn't really matter wether its 1, 1.5 or even 2 bar but you'll find a referance point is very helpfull later. Once the co2 is coming out of the diffuser you can set the required rate by using the needle valve. You'll find that after any adjustment it will take a while to settle down to its new rate so be patient whilst tweeking it. Thats pretty much it.
Its quite common for the output pressure of full canisters to fluctuate a bit when first used and again when nearing empty so moniter the situation closely at first but once you get used to using pressurised co2 it becomes a lot easier. To be honest I rarely change the setting these days on my needle valve even when swapping out canisters. Instead I tend to use the coarse valve on the reg and that mark I told you about on the dial, on the D-D set I find it to be very acurate and reliable.
Make sure though that you get and use a drop checker there is a very usefull tutorial on the subject here it really is your best friend when injecting co2.
http://ukaps.org/forum/viewtopic.php?f=34&t=467
If your set only came with one dial it is the output pressure dial. The high pressure dial (or canister pressure) is available seperatly, if my memory serves me right I paid about £11 for one from the D-D spares dept. Its usefull to know when the output pressure starts to fall as this is an indication of the canister starting to empty. For reasons I can't explain (i'm sure someone on here could) when canisters become nearly empty they sometimes release all of the remaining co2 in a kind of final spurt as it were. This is commonly refered to as a bottle dump and can happen quite quickly and raise your disolved co2 up to levels that can kill your fish through gassing. I don't mean to be alarmist but its somthing that anyone using co2 injection really should be aware of.
Regards, Chris.