sumped 20 long with mag 5 return pump?

[bdevillier]

i'm in the process of upgrading my 10 gallon reef to a 20 long with a 10 gallon sump. i have a mag 5 pump thats not being used and i was wondering if it would be too much pump for my 20 long? i plan on running 2 returns off of the one pump. i used the head loss calculator on this site but it only gives you the option of 3/4" pipe. with the info i entered into the calculator it gives me a total of 4.88 ft of head and 254 gph. does anyone know how much the gph will change by going to 1/2"?
i was also thinking about using the returns for my flow and not running my powerhead to make the tank a little more nem friendly. any thoughts? sorry if i seem like im rambling but i'm trying to type and take care of a fussy 3 month old at the same time. its only taken 20 minutes to type this. lol. thanks in advance

 

[muhli]

I think you should run a "t" connector off the return line. That way not only would you be able to adjust the return rate, but you can use that to feed water back into the sump or refuge if you have one, or a reactor if you choose to run one

 

[bdevillier]

i was thinking of putting a t and ball valve to flow back into the fuge and allow for adjustment of the return rate. i'm just wondering if i should run two 1/2" returns or two 3/4" returns and will i be able to get the flow i need to eliminate my powerheads? thanks for the reply