Managing chemical addition with a auto acid feeder?

[JJoe]

My pool has automated acid feed (Hayward CAT controller w/Stenner acid pump). Pool requires regular acid additions to maintain pH (I keep pH at 7.6).

I have the Stenner set to give low rate doses (set at 1.5, 10 is max dose per "pulse"). The acid is injected into only return line (4 inch, pump is roughly 375gpm). Return line is linked to multiple pool inlets spaced evenly throughout perimeter of pool (3/8" holes in stainless guttering, 100 total as a wild guess).

Eventually my alkalinity gets low and I have to add sodium bicarb (when alk gets to 40 I raise to 70 or 80 max). Sodium Bicarb is broadcast into deep end (12ft). Supply to pump is through 5" or 6" line (can't remember which) from 2 main deep end drains and perimeter gutter overflow. Supply lines gravity flow to surge pit, pump pumps from surge pit.

Question is, should I turn off my acid feed when I need to add Sodium Bicarb? Or can I just let it run because the rate is so low, pump flow is high, and inlets are evenly spaced?

I was instructed to always turn off the acid feed until sodium bicarb is fully mixed (6 hour pool turnover). When I do that though, pH usually rises and then Stenner has to play "catch up" to correct pH.

I guess question could also be relevant to chlorine additions (applied to deep end).

So what say you? Turn off acid until additions are fully mixed? Or leave on because acid doses are small and highly diluted?

Thanks in advance.

 

[kimkats]

I know what I think but want to bump this up for more eyes.

 

[Jimrahbe]

Joe,

I can't answer your question, but is the 7.6 pH number a mandatory number??

If not, I would try running it at 7.8, which should take a lot less acid and not drive your TA down so quickly.

Thanks,

Jim R.

 

[riley00dog]

I’m not sure what the correct answer is. You would be best to call the manufacturer to ask them. We have a similar acid dosing system and don’t turn it off for additions. I believe that by the time the minute amount of acid make its way into the pool it is incredibly diluted. My thinking is that since you can swim with it dosing it would be fine to make additions too. These are just my thoughts though and not advice on what’s actually correct. If you find out from the manufacturer could you post back?

 

[JJoe]

7.6 is not mandatory. Can do 7.8, just settled on 7.6 to give a little more cushion before it hits 8+.

System keeps pH very consistent though, and I have eliminated a constant source of aeration, so raising to 7.8 is worth a try. Thanks

 

[JJoe]

I’m not sure what the correct answer is. You would be best to call the manufacturer to ask them. We have a similar acid dosing system and don’t turn it off for additions. I believe that by the time the minute amount of acid make its way into the pool it is incredibly diluted. My thinking is that since you can swim with it dosing it would be fine to make additions too. These are just my thoughts though and not advice on what’s actually correct. If you find out from the manufacturer could you post back?

I think it should be diluted enough too. Not sure what consequences would be if it is not though.

System also has an inline bromine feeder. Acid and bromine were both injected into same line, at nearly the same spot. It ran like that for over 2 years, with acid and bromine feeding at the same time. No disastrous consequences, but did have issues with maintaining water clarity. Clarity issues may not have been caused from setup/operation of both, but maybe?

Not using the bromine now, but might look to some kind of chlorine auto feed, and would really like to know the pros and cons and risks. Checking with manfacturer if the CAT controller is good idea, thanks