Pentair 4-Gallon Acid Container Usable Capacity (521378) or (522472)


Gold Supporter
Jul 3, 2018
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Recently I had a need to determine EXACTLY how much “usable” liquid is available with regards to the Pentair 4-Gallon Acid Container when it is full.

Without going into a whole lot of detail at this time, I am in the process of transitioning from utilizing a Pentair IntellipH Acid Dispenser System to using a completely different chemical controller that is software driven and administers acid dosing predicated on pH sensor/probe readings versus a predication based solely on “time,” as with the IntellipH.

Note: Please don’t get the wrong impression that I have anything to do with the actual development of the controller software. Ha, I am light-years away from possessing any of those type of skill sets. I am grateful to have the opportunity to merely assist and to participate in the beta-testing of this new controller software however. It's a lot of fun to be able to play with a new platform that does so much and which is really changing my whole perspective on swimming pool automation, sensor and chemical control capabilities..

This newer system is similar in many respects to the Pentair IntelliChem controller. To include all of the very same safety features found in the IntelliChem system as well as the IntellipH system. But in my opinion, this new controller performs with much more versatility, overall flexibility and “user-friendliness” than the commercial “off-the-shelf” systems and without all of the Pentair imposed restrictions and limitations.

However, I determined that I would continue to use the Pentair 4-Gallon Acid Container and its associated peristaltic pump with this new system. The 24VDC pump is energized via a Sequent Microsystems I2C 4-relay (10A/240V) Raspberry Pi Stackable Card and with inductive load relay protection provided by an LC Technology RC Snubber Module.

So, I needed to determine the “usable” liquid capacity in the container so that the chemical controller software can keep track of the real-time amount of “usable” liquid in the container since it tracks the amount of liquid dispensed. In other words, it would cause inaccurate tank measuremen2020-12-26_15-24-41.jpgt readings to input a container capacity of X within the controller software, when in reality, all of the liquid in the container is NOT usable. By providing the controller software with more accurate information, the controller software can better indicate a more accurate real-time amount of usable liquid remaining in the container. And by which, it will NOT indicate “or consider”, the liquid that is unusable. Hmmm, the ole’ GIGO scenario.

At this same time, I also needed to replace any acid that remained in the tank with pool water temporarily so I can complete the beta-testing on this specific feature of the controller software as well as conduct final testing on the relay as well as the snubber circuit module in order to confirm compatibility. I needed to perform this real-world testing while at the same time NOT creating a possible acid over-dose situation in the swimming pool in the course of these testing trials.

Consequently, I performed both requirements at the same time. In the event that anyone might have a similar project on the horizon or has a need for the following information, here is what I determined…

1. The TOTAL capacity of the Pentair Acid Container is 4 Gallons (15.1 Liters). Adding 4 gallons to an empty container will bring the level of liquid in the container to the very middle of the protective grid or to the bottom of the container top mounting lip.FC03CD1B-BF1D-423A-BF9E-264F2A50E1D8_1_105_c.jpeg
2. However, of these total 4 gallons. I determined that there is 10 ounces (295.7 mL) of liquid at the bottom of the canister that is unusable. This is due to the fact that the suction tube and plastic filter screen do NOT quite go all the way down to the bottom of the container. Hence the “usable” amount of liquid in the canister is 3 Gallons, 6 fluid ounces (3.375 gallons) or 11.8 Liters.​
3. By way of these measurements, I determined that the vertical sticker that is placed on the side of the container is inaccurate in its representation of actual liquid increments within the container.​
4. On pp 1 of the IntellipH Acid Dispenser System Installation and Users Guide, it refers to the “Storage Canister” as “3-1/2 Gallons.” I realize that this stated value in the users guide is off by only 2 ounces but I’m just stating the fact that in typical Pentair fashion, information found in Pentair documentation is NOT always accurate and in many cases, incomplete as well.​

Note: I assume that the same numbers defined above also apply to the Pentair 4-Gallon Chlorine Container (521397.) The only difference that I could find between those two part numbers (tank only), or between the two part numbers with a mounted pump (522472 vs 522473), is the fact that the color coded stickers placed on top of the lids are different.

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