Acid Pump Flow

woodsage · Jun 15, 2009

I installed a Stenner variable speed acid pump with a #1 pump tube that discharges a maximum of 5 GPD on a #10 pump setting (maximum). I'm diluting the acid 4:1 with water. I'm also using a Goldline controller which has a 2 hour maximum run time for the acid pump.

I'm trying to lower the pH from 7.8 to 7.6 and the acid pump times out and I have to reset the controller every two hours. Are these systems designed to just "maintain" pH level or can they "lower" the pH level. All that is happening is the pH is not rising, but I can't lower the pH level.

Do I need to increase the concentration of acid or change the pump tube to a #2 which discharges up to 17 GPD to have the pump actually lower the pH level or manually add acid to get to the desired pH level and then have the acid pump "maintain" that level?

JasonLion · Jun 15, 2009

How large is your pool, and what are your TA and Borate levels?

woodsage · Jun 15, 2009

I have an outdoor, 21,000 gal plaster pool, screened cage, no pool cover, solar heat, SWG, cartridge filter, sense & dispense system, Goldline controller in SW Florida and I like to keep the FC level at 4.0.

I'm going to have to get back to you on the borate level since I don't have test strips for reading borate levels. The TA is 105.

JasonLion · Jun 15, 2009

If you haven't intentionally added borates, then the borate level can be assumed to be zero.

Your pool is a fairly common size, and your TA and Borate (presumably) levels are reasonable. I was concerned that the acid demand might be much higher than the controller is designed for, but that does not appear to be the case. The controller is designed for a 5 GPD pump and a 4 to 1 dilution. So you appear to be doing everything correctly.

The only remaining unusual possibility, fairly unlikely, is if you have fresh plaster. Fresh plaster, especially in the first month, has an extreme acid demand, that would trigger the maximum run time exceeded.

I don't have experience with the Goldline PH regulation system. I have used the similar AutoPilot Total Control System. The AutoPilot unit has a setting to shut down acid feed when the PH does not come into range quickly enough. However AutoPilot recommends that this setting be disabled on "larger" pools, which seems to mean anything with 10,000 gallons or more.

It is perfectly possible that your unit will be able to maintain the PH if you get it into range manually. The system is fairly new, and might still have bugs that need to get worked out. Being unable to recover from high PH doesn't completely surprise me as a possible bug in the controller. It can be difficult for a controller to distinguish an acid feed problem from the PH starting more out of range than expected. It is also possible that they have a setting similar to the AutoPilot setting that should be set to disable to acid over feed shutdown option, though I don't see any mention of it in the manual.

There are two additional possibilities. There might be some problem with the acid feed, that prevents it from actually feeding acid into the pool. This is difficult to completely rule out. Have you checked that acid is coming out of the acid feed tube when it is not connected to the injector? Sometimes it can take the system an extra long time to fully prime, which the controller would read as an acid overfeed problem. It is also possible for the acid intake inside the tank to be too high, causing it to draw in air instead of acid.

The second additional possibility, though almost impossible with a new unit: the PH sensor tip can get dirty, causing it respond to PH changes very slowly, or not at all.

woodsage · Jun 15, 2009

I do not have fresh plaster and the pool is about 12 years old.

I did remove the injector and at the 5 gpd setting the acid is a steady drip from the injector.

dschlic1 · Jun 15, 2009

I calculate that you acid feed system will pump about 13 oz of un diluted acid inot your pool in two hours. Using the pool calculator it looks like this is just enough to drop your pH by 0.2 units without any other changes (ie SWG off etc). So it looks like you will need to increase the capacity of your acid feed system.

woodsage · Jun 15, 2009

I get 27+/- oz. per hour. Here is my math: 128 oz per gallon X 5 GPD/24 hours=26.67 oz per hour. Is this not correct?

JasonLion · Jun 15, 2009

The acid pump puts out 26.67 oz per hour. But dschlic1 was talking about the equivalent amount of full strength acid. Since there is a four to one dilution, that would mean dividing by five, which gives 5.33 oz/hour of full strength acid equivalent.