Logistics for Change from Cal Hypo to Sodium Hypo


Sep 20, 2011
My non-profit org has an indoor 100,000 gal pool that has been using granular 65% Cal Hypo for decades. I'm looking into switching to liquid Sodium Hypo. Primarily due to the hard water issues that are a pain - Hardness test was over 1200 last week! Refill water hardness is already 250-300. But also because we need to meter chemicals.

We have no local suppliers nearby, but have located a company willing to drive 2 hrs to bring the drums to us. The pool companies can't help much as their systems are not designed for a pool like ours, and I'm not interested in being tied to a branded puck.

So now I'm trying to anticipate cost changes and logistics needs of the different chemical - It looks like we will be using about 5x more bleach daily - a little less than 102 oz of bleach daily compared to 21oz of CalHypo for a 1ppm rise in FC.

It looks like a metering pump running 0.2 GPH (5 gpd) would more than do the job. Line pressure is low as were pumping into a 6" PVC line to the pool - I think we're at 15 psi according to a gauge (if it's working properly...) I'm slightly be worried about throttling down enough do deliver a small amount , perhaps 0.5-1 gpd - 10-20% of it's stated output. Perhaps a 0.1GPH would be a better choice. Some day, if we ever had the funds, it might be nice to have a controller on it, but until then we're all manual. We do already have an outlet that is interconnected to the pump - if circ pump is not running, the CL pump will be off.

Any issues pumping direct from a 30gal drum? To they make a feed-through cap we can use on the drums? Or would we need to transfer to a separate tank/system like a BlueWhite Star III?

Another other option is to keep with the CalHypo and mix into solution ourselves, but I'm assuming that will be a maintenance nightmare trying to keep an agitator running above the tank. Opinions?

Note - We do not use CYA for this pool as rules around Crypto prevent us from doing so inside. No ozone, UV or Cl generator either. Filtration provided by a gravity fed drain to DE filter with the pump providing vacuum for the filter and pushing the water back to the top of the pool.
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TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Do you already have an acid dosing system? I've got to imagine with cal-hypo, you were lowering pH a lot.

No major differences between cal-hypo and bleach except you might use a little less acid with liquid chlorine injection. Most of the metering pumps for LC can easily overcome a 15psi line pressure - there are residential Stenner pumps that have a max pressure limit of 100psi. If the drums have the proper connections, then the metering tube could go right into a chlorine drum...all depends on what they are shipping to you. Obviously staying away from transfer pumps and multiple containers would make the system a lot less of a hassle.

You can't really make LC with cal-hypo. The pH of the resulting mixture is usually too low and that makes the chlorine in solution very unstable. Plus it's just not convenient to try to make it yourself and manage it. Best bet is to get those tanks delivered with the proper connection so you just have to plug and go.
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Sep 20, 2011
Glad to have the confirmation that premixing cal hypo is not the way to go - We certainly won't peruse that anymore.

We have no system for any chemical additions at the present, so I'm unfamiliar with the dosing pump side of things. It looks like you can set a specific value and they'll simply run that until you change it, unless you connect to an ORP. Yes - I knew the pressure wouldn't be an issue, but I'm not as certain how fine of an adjustment we'll need on the pump - I assume appropriate ranges would be 0.025-0.2 gph for NaOCl , 0.01-0.1 gph for HCl based on our past use, but confirmation would be great -I presume the ORP controller would just turn on/off these units at the rate set, as opposed to changing the rates dynamically based on measured need.

Still waiting to get numbers back on the NaOCl drum costs, percent, etc. -- I realize that I'm likely already using the cheapest form of Chlorine (that's not gas cylinders) -- 100 lb drums of cal hypo now costs me $200 ea delivered. That seems to be the 'in pool' equivalent in the water to 62 gal of 12% bleach, so I'm hoping I can get 4 - 15 gal carboys, 2 - 30 gal or 1 - 50gal drum for somewhere in that range, but currently have no idea what it'll come to.

I hope that we can change over to NaOCl asap and just get a basic pump for now then perhaps upgrade to add a controller and acid dosing sometime soon.


Silver Supporter
Nov 23, 2017
Port Orange, FL
I'll preface this by saying I know little about indoor and/or commercial pools. It seems the chlorine demand is rather low considering the pool size because the pool is indoor without significant UV exposure. Is a SWCG not an option under these circumstances? Just asking the question for my own edification.


Sep 20, 2011
It would definitely be an option, however the start-up costs are considerable and as an entity that relies solely on donations (we do not charge fees for service as our clients largely could not) Thus it is money we do not have.

I could plead the case to a grant institution that the SWCG would be a safer choice immediately (less caustic materials on hand) as well as potentially reduce operating costs. It will be something we'll look into more before we'd go whole hog into full chemical controller. My guess is that we'd have $4-5k into a SWCG compared to $2-4k in chemical controllers including installation for both. But we have many more pressing needs we need them to fund!


TFP Guide
May 10, 2017
Hays, Kansas
Better get a pump in the 10 gpd area, maybe a variable drive stenner. To control it just spend $10 on a timer and sync it with your pump schedule. You can always add more or less time. Stenners are great run from the drum into the pump. Diaphragm type pumps work great but need to be lower than the drum and the drum will need to be on its side and you need to bleed air in them every once in awhile.

With a stenner get the biggest drum.


Sep 20, 2011
We have to circulate water 24/7 no timer here - I've considered installing a basic IOT outlet (always has the correct time, can monitor & control remotely) but it's one more point of failure in an area with high humidity area and corrosive chemicals. I’ve reached out to 4 companies recommended by our water treatment plant to deliver 12-15% NaOCl and prices are coming back around $2.50/gal in car boys & drums. I’m currently paying $3.30 per gal equivalent ($200 for 100lb drums of 65% cal hypo which equals about 60gal 12% bleach). So there's wiggle room for extra delivery fees. One company required a $400 minimum per delivery -- 4 - 53 gal drums for a total of 212 gal which is likely to last 4-7 months depending on bather load.

Pump is ordered and on the way. I’m debating injection port locations. Obviously they will be placed after the all other equipment. It’s also good to know our pool is a long rectangle 35x75 and inlets are supplied via a 6” main that divides into 2, 4” runs that each feed down one of the long sides. Huge lines that the allow our water to flow into the pool at low velocity (2.75fps in main and 1.5fps at inlets)

In considering the location to install the injection ports I could place it in the 6” line to evenly feed both sides of the pool, or one of the 4” lines. The main perceived advantage of the 4” line placement is that if an acid feeder were to be installed later, it would be placed into the other 4” line, thus fully eliminating potential for chlorine gas buildup in the lines if someone disabled or bypasses the interlocked outlet the pump should be powered by.

Alternately, I could place the Chlorine feed in the main and the HCl in a 4” line but well away from the Bleach (like 20’). Thoughts?
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