Cost Comparison of Chlorine Sources


Well-known member
Jun 22, 2015
Phoenix, AZ
This makes these sources of chlorine quite a bit more expensive then Cal-Hypo and bleach and chlorinating liquid.
I just wanted to say that based on the raw numbers, it's true, but I just got my pool replastered, and it actually saved me money because I got to buy less acid until my CYA hit 60 and then I quit using the pucks.

I also cringe when I hear that people are adding stablizer to their pools. Why not get the benefit of chlorine along with the stablizer and save the work of hauling bleach jugs and the expense. I'd like to see the math between stablizer + bleach and dichlor/trichlor. My fill water is ph 8.0, so is the acid from trichlor/dichlor not possibly offset?

I'm just really super cost conscious and I want to do things the cheapest way possible. I have my doubts about SLAMing as well. I think there should be some discussions before people start racing out and buying bleach and reagents. My fill after the replaster was an incremental $45 on my water bill for 18K and some of that was household useage so when the bleach expense starts to exceed that cost, I'd like to know what other factors might make draining and refilling a bad idea.

Besides my possibly misguided belief on ever buying stablizer, I also can't figure out why anyone would ever want to buy the equivalent of hardness+. My thought is get the cal-hypo. For me personally, I would never buy either because my fill water is 11 grains of hardness, and I think that works out to really close to 200 ppm. PoolMath says I should be at 250 to 350, but does it really kill me to wait for the CH to rise from evaporation? Since 3/4 when I filled the pool, my CH has risen from 200 to 250 in 2-1/2 months.

Divin Dave

TFP Expert
LifeTime Supporter
Oct 2, 2013
Longview, Texas
The reason we recommend folks to add stabilizer, is because the TFP doesnt recommend using Trichlor pucks as a primary source of chlorine.
We teach folks (or at least try), to only add what the pool needs.

A pool with 0 CYA will suffer a lot of chlorine loss due to UV. the larger the pool volume with insufficient CYA, the more dollars are lost to UV. Using pucks as a main source of CYA may take a while to get to a level to provide suffienct buffering effect. To prevent those wasted dollars worth of chlorine, we recommend to add stabilizer to minimum of 30ppm and use liquid chlorine.

Also Sooo many people come to TFP looking for immediately help from algae, and almost always, their CYA is either very low and they cannot keep chlorine in the pool, or it's through the roof due to using trichlor pucks and there is not enough FC to overcome the buffering effect of the stabilizer.

If a pool owner wants to use trichlor and knows what is happening and what they are adding and when to stop using them, then there is nothing wrong with that, other than wasted FC to UV. A lot of us here use them if we go on vacation or out of town temporarily because we understand whats going on. We consider pucks the devil for uneducated pool owners, but for an educated pool owner, they can be very useful.

TFP really is focused on teaching of pool chemistry. There are many posts in the Deep End and Chemistry 201 for those folks who are interested in the science part of it.

As for draining the pool vs. slamming to save $....
In many parts of the country, there are ground water issues which pose problems with hydrostatic pressure. Depending on locale, it can be risky to drain a pool if a pool owner doesnt have a hydrostatic valve. Many pool owners have no idea what a hydrostatic vavle is, much less any idea that their pool can pop out of the ground due to hydrostatic pressure.

Also, plaster is meant to be underwater. If a pool owner drained the pool and the lollygagged around with cleaning, sanding, acid washing or whatever, and didnt fill the pool back up in a reasonable amount of time, the plaster could be damaged due to exposure.

For vinyl liner pools, the water should never be drained any lower than having 6 inch depth in the shallow end. As the water gets lower, the weight of it starts pulling on the top part of the liner. Most oven, they either rip, or the liner shifts and becomes displaced with tons of wrinkles which can never be worked out when refilling and the end result is an unhappy owner with big ugly wrinkles in their liner.

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
San Rafael, CA USA
After a new or re-plaster job, the use of Trichlor pucks is reasonable for the reasons you stated, mostly that you know that acid will be needed to keep the pH from rising as much and that you need chlorine and to build up CYA. However, one must keep any floating feeder away from plaster surfaces because that acidity can be very damaging to plaster in general, but to new plaster in particular.

As for opening a pool and needing to add CYA, that's a different matter. If one already has Trichlor pucks, then of course it may be reasonable to use them, but one doesn't need the extra acidity of the Trichlor so when factoring in pH raising products the costs no longer swing towards using Trichlor as much though getting the CYA helps some. It's a slower process to build up so initially it may be more difficult to maintain the chlorine level unless one uses more pucks (that's true in the plaster case as well). So this case is more of a gray area.

As for Cal-Hypo, if one needs to raise the CH some but not a lot, then that is reasonable to use. If one needs to raise it a lot, it may take too long using Cal-Hypo and one doesn't want their saturation index very low for months on end. Same is true for waiting for evaporation and refill. However, as you point out, it doesn't kill you if it's low for not that long. It would be different if your CH were 50 ppm, for example. Being at 250 ppm is far less risk to start out. This is where scientific principles meet common sense.

There are no absolutes here. The main reason that people are told to use pure CYA to add CYA, to use calcium chloride to increase CH, etc. is for simplification -- each product addressing each need separately. It's easier to understand from a dosing and calculation perspective for newbies. However, once one gets the basic concepts down, then using chemicals that have multiple combination side effects can certainly be done if one understands them (as you do).

There are also multiple ways of managing CYA increase from Trichlor pucks. If water replacement were cheap and had no environmental consequences and one had a vinyl pool so didn't have extra costs of needing CH (or one had a plaster pool but fill water high in CH), then water dilution would be a way of being able to use Trichlor (plus a base to maintain the pH and TA) though at first when the CYA is very low one uses a lot of Trichlor to maintain the chlorine level so one has to figure that into the costs so may make more sense to use some pure CYA initially. The same is true for using supplemental algaecide products. If one isn't using HEDP metal sequenstrants and doesn't have a lot of evaporation and refill with water containing phosphates, one may be able to use a phosphate remover and then target a lower FC/CYA level to save perhaps half the chlorine compared to the levels in the Pool School that work regardless of algae nutrient level.

These combinations and alternatives are advanced concepts that inevitably get fouled up by newbies, but that does not mean that someone knowledgeable and experienced can't use them. In particular, pool services often have no choice but to use some of these techniques because they are not visiting the pool every day or two to add chlorine. Some do avoid stabilized chlorine, but then have large swings of FC over the week (e.g. 14 ppm FC to 4 ppm FC).