Return Pump Question

[fernalfer]

I currently have a Sicce Syncra 5.0 (1,321gph) max head height 12.6ft. I have a Dual Oveflow120 gallon tank with obviously 2 returns which split after the pump. I'm looking to change this into 2 Return pumps for redundancy in case one pump fails. The 2 smaller pumps i'm looking at is the Reef Octopus Varios 2 (792gph) each. Head hieght 13ft.

Do you guys think they will have similar flow?,going with the 2 smaller pumps then the 1 bigger pump?

i also like the fact that the Varios pumps put out 25 watts each equaling 50 watts as opposed to the 105 watts the Sicce puts out.

 

[Goodair]

Having 2 return pumps is more redundancy, which is always good but you need to look at the charts and see what flow you get after all your headloss.
2 pumps with ~ half the flow of 1 big pump will not be the same after x amount of headloss.
For example:
1 1300gph pump at 6'loss gives a max of 700 flow.
2 800gph pumps at 6' loss gives max of 300 flow each.
Those numbers are made up but should give an idea what I mean.

The max head height of a pumps means that at that head height, there will be 0 flow. Elbows also factor into this. There are hydrolic formulas to find loss but tanks dont need to be precise and there was a post giving a rough estimate how much you lose per elbow which is sufficient. Forgot where it was but you can prob find something by searching.
Hope this helps and I'll try to answer anything else if I can!