Variable speed return and ato ?

[SALTYwaterDOG]

Hello fellow reefers I recently installed a variable speed return pump. Now the level of the return section of the sump changes a cording to the speed of the pump. The return section is were I keep the ATO censor. So now I'm at a loss as to were to put the ATO censor. I know the answer is to this has to be easy, but I having a mental block. Where do I put the ATO now?

 

[thegrun]

It needs to stay in the return pump section, that is the only section where the water level will change with evaporation. You need to run the return pump at a constant speed. You pick the amount of flow and then stay with that amount, you cannot change the speed at different times of the day or your salinity will fluctuate. I suppose you could vary it a little bit but there will variations in your salinity if you do so.

 

[ca1ore]

I agree that the return pump is best run at a constant flow, however, the problem you describe is similar to when some of us used to run surge devices that involved a separate reservoir that would fill and then empty. The ATO answer now, as then, is actually to do nothing. It will self correct. You will probably get fewer, slightly larger ATO fills each day, but not enough really to affect salinity as long as the main pump is cycling through the various different flows relatively quickly (say at least every few hours). What happens is that when the pump is running at its highest flow rate, the return section water level will drop, and that's when the ATO triggers.

 

[SALTYwaterDOG]

Thanks guys I kinda thought there wasn't an alternative. I'll just set it it and forget it. I was hoping to run a higher turn over during the day.

 

[thegrun]

You could give it a go and see what the salinity drop actually is. Stabilize the tank's water flow at the lower speed, read the salinity and then crank it up to the highest speed you planned on using, let your ATO add the needed water and see what the drop in salinity actually is. I doubt if it is 0.002 or less that it would make any difference at all to your livestock. If it is more than that I would not advise varying the pump's speed. It uses less energy to vary the water flow with in tank powerheads and leave the return pump at the lower speed, which is what I do.