Trichlor versus bulk stabilizer - cost

[dayhiker]

The Cal-Hypo conversation in Chem 201 got me to thinking about trichlor cost verus bulk stabilizer. Does this analysis look correct?

From chemgeeks post, a 10ppm increase in FC relates to a 6ppm increase in CYA.

My pool is 24k gal. It takes a 3.7 ppm increase to get me to 182 oz of bleach. A 182oz jug is around $2.50 if memory serves. It takes 13 oz of trichlor to be the equivalent to the 182. There is probably some rounding on that 13 number and since we're rounding the little number instead of the big one, it might void the analysis....I'll continue anyway.

10ppm of FC = 6 ppm of cya, thus a ratio of 0.6, so .6*3.7 FC = 2.22 ppm of CYA. It takes 6.4 oz of CYA to increase 2.22ppm.

From aquasuperstore, it's $35 for 10# of trichlor or 3.5$/#. It's $39/8# of stabilizer at Leslies or $4.875/#.

To get 13oz of CL from trichlor you have 13/16*3.5 = $2.84 which is a little more than the bleach. You get 6.4 oz of CYA for "free"
To get 6.4oz of CYA from bulk you have 6.4/16*4.875 = $1.95.


So, if you're short of CYA and work the number back from a 1 jug equivalent, you'd have $2.50 + $1.95 = $4.45 for bleach or $2.84 for trichlor alone.

Let's relate $/ppm of CYA, tri: $2.84/2.22 = $1.28/1ppm; bulk: $1.95/2.22 = $0.88/ppm. So, if you're a swg person and rarely use bleach (but do on occaision) like me then it makes sense to keep buyiing bulk stabilizer and grabbing a jug of bleach when needed. If you're using lots of bleach then it looks like it makes sense to supplement with trichlor at the beginning of the season.

Am I missing anything?

 

[JasonLion]

You forgot to compensate for the PH reduction caused by trichlor. You should add the cost of enough soda ash to raise the PH/TA back up to where it was after adding the trichlor.

The other aspect, is that using trichlor as a source of CYA only adds CYA very very slowly (assuming it is added at a rate based on your chlorine demand). That means you could spend a significant amount of time at a low CYA level, which has its own costs.

 

[dayhiker]

Good to know, thanks.

 

[chem geek]

I did a cost comparison in this thread that you might be interested in.

 

[PaulR]

You forgot to compensate for the PH reduction caused by trichlor. You should add the cost of enough soda ash to raise the PH/TA back up to where it was after adding the trichlor.

Yes, trichlor should really be considered a 3-way chem, replacing bleach + CYA + MA. And if the MA equivalent is no more than your normal MA consumption, there's no extra cost for bringing pH/TA back up; in fact you win from lower MA use. That has been my usual experience. People starting from a more stable pH would have to compensate.

The other aspect, is that using trichlor as a source of CYA only adds CYA very very slowly (assuming it is added at a rate based on your chlorine demand). That means you could spend a significant amount of time at a low CYA level, which has its own costs.

True, using trichlor as a CYA source should be done only when slow CYA increase is okay for other reasons (e.g. in warm-climate winter or early spring when FC consumption is low anyway but you don't actually close the pool).
--paulr

 

[guamguy]

I've been using dichlor to raise CYA in my pool. I started out with brand new water when I moved into my new house. There was a BUNCH of dichlor "shock" in a storage closet when we moved in, so I've been using that 'cause it's free. My TA is about 130, so it could stand to drop a little bit, and I can raise the Ph by aeration with the spa easily enough. So I use mostly 6% bleach, and some (free) dichlor now and then to adjust CYA.