Hi Mavgi,
Welcome to Reef Frontiers! You've got a couple of questions going on here all at once...but I'll try to help you out with the one regarding the return pump.
The
Blueline 40 HD-X External Water Pump is really just a renamed/relabeled
PanWorld 100PXX-MD40X External Water Pump - 1270gph. Its good to keep this in mind when looking for replacement parts, etc....The Blueline is just Champion Lighting's label on a Pan-World.
Its a good pump, but its not pressure rated, meaning you will lose alot of head pressure when the pump has to push water into smaller openings, through bends, (90's or 45's) and when head pressure increases, ("uphill" so to speak). This isnt a problem, its just something to be aware of.
There are many flow calculators out which will help you determine exactly how much water you will be moving when you configure your plumbing. One thing you need to always keep in mind is the inlet/outlet diameter of your pump. In this case, its 1 inch inlet/outlet. Since this is a non pressure rated pump, if you reduce the outflow to 3/4 of an inch, (the largest size of Loc-line available, you will seriously choke your pumps return flow. This will create more back pressure on the pump will eventually shorten the life of the pump.
However there are many ways around this....
The purpose of a return pump is just to bring water from the sump, back to the tank. You're not really worried about how it gets there, just that it does, if you can make the water flow more chaotic, then great, if not, no big deal.
With that in mind, a standard RR 120 has two 1 inch overflows(drains) and two 3/4 inch returns. If you run one pump for both returns, you will a single 1 inch outlet (pump) flowing through two 3/4 inch returns. I'm not a fluid dynamics guru...but I believe that would be close to a single 1 inch return. Please understand that due to surface area of a circle, (math here...not necessarily my strong suit) two 1/2 inch drains cannot handle the flow from a single 1 inch diameter drain. I believe it requires something like four 1/2 drains to equal the flow capacity of a single 1 inch drain.
Reedman, ( a member here), is very good at this sort of thing...might want to give hima PM about the whole issue. He can correct any misinformation I might have inadvertantly given you.
One thing I would definately reccomend with you future set-up...allow for redundancy and have a back up for EVERYTHING VITAL to your tank....IE PUMPS, HEATERS, and COOLING SYSTEMS.
I woke up yesterday and both of my return pumps (One Iwaki and one Mag 7) had quit working. I got them both working again, but I was not happy at having to drop everything I had planned for the day to deal with this. If I had a second pump on a shelf, all I would have had to do was slap the new one on, and fix the old one at my leisure. Instead of being an emergency, it owuld have been an annoyance....
Food for thought.
Nick