ATO based on Conductivity/Salinity

[BoxesOfTheSea]

Is anyone here using a conductivity probe to trigger an ATO pump through a controller? I would think that it would be safer than depending on a float switch.

 

[el_pinguino]

This is usually not done. The general consensus is that conductivity probes are not reliable enough for this application. Biofouling causes sensor drift and it would need to be cleaned and re-calibrated frequently.

 

[Coral Dilema]

I've always been a fan of a mechanical float valve in the sump in the chamber with the return pump. Simple, reliable, never had a problem with one.

 

[ca1ore]

Even if you keep the probe perfectly calibrated, I'm not sure the level of accuracy is adequate to be adding water baed on the salinity readings. One thing I have noodled over is whether to use my apex salinity probe to 'select' which reservoir to use for a particular topoff. If the salinity probe reads below a certain level, then topoff water, still controlled by the float, will come from a reservoir of salt water; if the probe reads above a certain level then topoff will be regular RODI.

 

[drsalomon]

I do the two reservoir Neptune ato and so far works great

 

[acesq]

I don't understand the need for a two reservoir automatic top off system. The only way to decrease salinity such that you would want to top off with salt water is to either over fill with fresh water (in which case the float valve should save you and you can re-calibrate your ATO), or you are losing salt water and adding fresh (in which case, you have a leak somewhere). Why two top off reservoirs?

 

[Steveb]

This is usually not done. The general consensus is that conductivity probes are not reliable enough for this application. Biofouling causes sensor drift and it would need to be cleaned and re-calibrated frequently.

That is the same info I received when I queried about it. I was toying with idea to use this for ATO in conjunction with a surge bucket since sump volume goes up/down with them.

 

[drsalomon]

Salinity tends to trend down with ski mate removal. Salt ato replenishes it. Most of the time ato draws from rodi.

 

[durango_doug]

A simple way to solve the problem would be to add a small amount of salt to your top-off reservoir. You could determine the exact amount of salt needed to maintain the tank's salinity by measuring the volume of skimate extracted vs. top-off water used during a set amount of time. This method seems less risky to me.

 

[Epicreefer]

I have used a conductivity probe based salt addition on freshwater systems many times and it works well for that situation. Basicaly an auto water exchange with ro causes water to overflow down the drain and then brine is added with a peristaltic pump to bring levels back up. These were for researchers so they wanted a stable conductivity with varying water supplies... In my experience, and talking to the manufacturers, in fresh water recalibration isn't necessary but in sw with similar setups, but water change was with separate sw tank, bio fouling has minimal effect short term and you just need to clean the probe every month or so. These were fish only tanks tho. I just use a simple rodi top off on my personal tank. In many reef tanks I've worked on typically the salt added from two part solution is much more than skim mate removal and I usually need to remove about .5% water volume monthly to adjust or water changes take care of it.

 

[acesq]

Salinity tends to trend down with ski mate removal. Salt ato replenishes it. Most of the time ato draws from rodi.

My salinity would tend to drift up due to 2-part addition, even with constant skimmate removal. But the amount of drift from either cause is so slight (unless you skim very wet) that setting up a separate ATO seems difficult at best. I just compensate during water changes. Its an easy calculation to adjust the tank salinity up or down a couple of points.