Hello,
So I currently run two return pumps, and I have dual returns. Now I’m not the best at piping and plumbing, but I’m really good at physics, and math. If you run two return pumps on the same line, you will have some problems.
First, as some others stated, it’s going to push water through the other pump. Even if both pumps are running, the one that has least resistance will still have backflow water pushing against the water it’s trying to push out. Your going to make the second pump work three times harder and it probably will fail. It’s not designed to do what your doing.
Have you thought of some simpler ideas but more effective. Example, yes I have two heaters in my sump and I need flow to keep the tank warm. However I have a back up that you can’t see. There is a third heater next to my over flow placed horizontally. It’s set at 75 as my main two are at 78. Now in doing my rock work, I am able to see the little light that comes on etc through the rock, but not much of the heater.
Secondly, well my hands and arms are pretty small, so yes I can always move and reach the heater if it fails. Plus I have four wave makers in my tank so it will still get flow somehow to the heater.
Another idea is to run one return pump like designed to. Then run the second pump but you could try soft plumbing and run it has its own line to the other side of the tank. I have seen large aquarium tanks do this as well. Their tanks only have one overflow but they need more flow. So they run a separate pump and line.
I run twin return pumps but they each have their own dedicated line. So if one fails, yes I have another one running. Yet, that’s not why I did it in the first place lol. I did it because it increase flow and pressure in my display, and gave me more options for flow and I could run the pumps at minimum. They do not have to work so hard to move that much water.
But, people are correct, return pumps don’t fail, if that’s your main worry your fine. Simply conceal a back up heater in your display tank, and you will have flow since you have wavemakers. You have a good idea, it’s just physics will work against you, and probably win.
Good luck in what you decide to do.
Sarah