VarioS-6 or 8?

mjk42 · Oct 14, 2025

Hello everyone!

Another question for help setting up my first tank as I am now taking a crash course in plumbing calculations with flow and head pressure for a return pump...

I am setting up a UNS r120 with 94 gallon display and 122 gallon total with sump. I am planning for a VarioS as they seem to have a generally good reputation and will link with the wave maker/Hydros controller. The plumbing setup is built into the tank system and has 5 vertical feet, 3 45degree angles leading up to a "Y split" into two returns each with a 90 and 2 45 degree angles. I'm no engineer but piecing together what I can find on the board, it seems like the Y split will reduce the flow and head pressure into the two returns so I'm estimating a total head pressure of about 8-9ft. There is also a manifold plumbed off the return line that I will plan to connect to a UV. I have no idea how to factor this in for flow reduction/head pressure for the main tank...

The VarioS-6 has flow sheet that would put out 790 gph with 8ft of head pressure (not factoring in loss from manifold)
https://www.coralvue.com/varios-6-controllable-circulation-pump
The VarioS-8 would be much higher at 1300gph with 8th.
https://www.coralvue.com/varios-8-controllable-circulation-pump
Both pumps are the same physical size and 36V but the 8 is higher watts.

I'm leaning towards the VarioS-8 which seems like it would give more than enough flow and would also allow me to run it at a reduced rate instead of full power.

Appreciate any input!

Klem · Oct 14, 2025

mjk42 said:
Hello everyone!

Another question for help setting up my first tank as I am now taking a crash course in plumbing calculations with flow and head pressure for a return pump... I am setting up a UNS r120 with 94 gallon display and 122 gallon total with sump. I am planning for a VarioS as they seem to have a generally good reputation and will link with the wave maker/Hydros controller. The plumbing setup is built into the tank system and has 5 vertical feet, 3 45degree angles leading up to a "Y split" into two returns each with a 90 and 2 45 degree angles. I'm no engineer but piecing together what I can find on the board, it seems like the Y split will reduce the flow and head pressure into the two returns so I'm estimating a total head pressure of about 8-9ft. There is also a manifold plumbed off the return line that I will plan to connect to a UV. I have no idea how to factor this in for flow reduction/head pressure for the main tank...

The VarioS-6 has flow sheet that would put out 790 gph with 8ft of head pressure (not factoring in loss from manifold)
https://www.coralvue.com/varios-6-controllable-circulation-pump
The VarioS-8 would be much higher at 1300gph with 8th.
https://www.coralvue.com/varios-8-controllable-circulation-pump
Both pumps are the same physical size and 36V but the 8 is higher watts.

I'm leaning towards the VarioS-8 which seems like it would give more than enough flow and would also allow me to run it at a reduced rate instead of full power.

Appreciate any input!

I would go with the 8, but I’m kinda biased because I own two of them… With that said, if you get the 8, you can always dial it down if there is too much flow. Plus an 8 will allow you to have extra flow for future needs. I’ve had mine for 8 years and they are excellent pumps. Just maintenance them at least once a year to make sure the little flow port doesn’t get clogged up. Most fail because that little port gets clogged and it fries the pump.

hers0109 · Oct 14, 2025

I would go 6 for that sized tank. I’m running a similar gph pump to the 8 (@ 70% power) on a 240 gallon system with many more turns and head pressure than that.

BeanAnimal · Oct 14, 2025

Always go with the larger DC pump if your budget allows. They tend to live a longer life when run at partial power. Unlike AC synchronous motors, the DC motors require electronic control. At lower outputs the transistors that control the rotation run cooler and have a lower failure rate.

mjk42 · Oct 16, 2025

BeanAnimal said:
Always go with the larger DC pump if your budget allows. They tend to live a longer life when run at partial power. Unlike AC synchronous motors, the DC motors require electronic control. At lower outputs the transistors that control the rotation run cooler and have a lower failure rate.

Good to know about the transistors running cooler. Seems like the large pump at lower power is the way to go. Maybe another simple question but how do you get a general idea of the flow rate when you are running it at lower power? Wont really match the pump flow chart provided in this case and the return is plumbed directly into the sump so the timer and bucket method would seem difficult. Just put the return pump flow a little lower than what the outflow can handle?