UV Pump in Sump Affects ATO Viability

[pianosdr]

QUESTION:
This is how basically everyone has suggested UV plumbing should be done if you are not going to plumb the UV return literally directly into the display tank itself, so how is anyone else with a UV plumbed like mine dealing with this issue?

CONTEXT:
I have a Sicce Syncra 7.0 pump sitting in my sump for my 91g RedSea Reefer 350. This pump is plumbed to a UV sterilizer, and as many different places suggested was the correct plumbing method, I have it plumbed to pump water from the main chamber of the sump (into the UV) and returning water to the return chamber. This is done to ensure the UV isn’t simply re-sterilizing the same water repeatedly.

PROBLEM:
I’ve noticed over time that this pump is causing inconsistent fluctuations - or even a *complete lack* of fluctuation - in the water level of my return chamber. This is a problem because my (Neptune) ATO system requires the water level in the return chamber to drop due to evaporation in order to trigger itself to add RODI. With the inconsistent or nonexistent return chamber water level behavior, the high water level sensor on the ATO is basically always covered no matter what, which causes upward salinity creep over time until I manually add RODI. I can even see the water level dropping in the rest of the sump while the return chamber level remains constant (or will sometimes drop briefly but then just as briefly fill back up).

CAUSE:
I have confirmed that the issue is definitely the UV pump. When it’s on, it seems to be preventing the normal water flow from the main chamber to the return chamber to occur, resulting in this issue. I can see this in numerous ways:

* constant upward salinity creep
* ATO logs show the ATO never activates over several days (it’s warm here so evapo is happening regularly throughout the day)
* Error logs show my high water level sensor in the return chamber is constantly on for days straight, or sometimes it will constantly activate, deactivate, re-activate, etc many times over without anything being added to the tank to cause the water level to fluctuate like that.

As soon as I turned the UV pump off, everything went back to normal.

 

[Quietman]

While the intent of the UV not refiltering water was good, the execution of that is causing you problems. With the pump discharging into the return section (if I read correctly) then you have another source of water into the return section instead of the sump baffles. This will cause the ATO to not work correctly as long as water being supplied from the tank. Makes sense with pump off everything corrects.

Ideally you discharge the UV into the tank directly. You can also put it direct in the return line (not optimal but it's what I do). Lastly having the UV supplied and returned to sump while least productive will still be much better than no UV.

 

[pianosdr]

I’m not sure I understand how it would be possible to return the uv line directly to the display without making it a giant eyesore…unless, like you mentioned, it’s plumbed to tie directly into the return line, though that’s just not an option for me for logistical reasons.

I suppose I will need to settle for just returning it to the same chamber the pump is in :/

 

[Serpentman2024]

Have the UV return to the same section of the sump you’re feeding it from and this shouldn’t be an issue. Because you’re actively pumping into the return section, it will get out of balance.

 

[Waters]

I agree.....I remove and return UV water to the same section of the sump. Water moves through the sump fast enough so that whatever water you are treating twice is very limited.