Tri-Chloro and Cal-Hypo ratio to achieve CYA control and pH balance.

[Ron Stordahl]

Our 66,000 gal in-ground outdoor pool operates for 3 1/2 months (roughly May 22 thru Sept 7). During that period we use Tri-Chloro and Soda Ash to achieve proper FC and pH, but CYA can reach 100 when we have another month before closing, requiring us to drain 50% of the water and refill. Quick research says Tri-Chloro's pH is 2.9, Cal-Hypo's ph is 11.8 (and without any CYA). Would there be some balance in usage of both to control pH and avoid the 50% water drain necessitated by greater than 100 CYA with only a month before closing? It seems to me that Tri-Chloro is more acidic than Cal-Hypo is basic thus likely still requiring Soda Ash to maintain a pH of 7.5. After our short season we drain the pool to below the plumbing to winterize. In the spring we remove the remaining water full of leaves, make repairs and often paint, then refill starting with fresh water.

I am wondering if the use of both sanitizers in the right proportion may be solve our CYA problem and have additional advantages regarding pH.

 

[Mdragger88]

There’s a caveat to the cal hypo- it adds calcium. Too much ch can be a problem.
Liquid chlorine only adds fc & a little salt & is the preferred method of manual chlorination.
It’s not hard to control ph with Muriatic acid. In fact it’s much simpler when each chem added only effects one parameter instead of trying to juggle the multiple effects of one chem.
Liquid chlorine for fc
Muriatic acid for ph
Stabilizer for cya

How to Chlorinate Your Pool

Before chlorinating your pool, you should know these simple tips. Learn the best way to add chlorine to your pool.

www.google.com

Pool Care Basics

 

[YippeeSkippy]

You're right.... if you can keep up on the balance. Trichlor *is* acidic. Folks using it and then stop can't understand why they're fighting their pool pH rising now.
CalHypo being base but you want to monitor your calcium levels.

Do you drain some routinely off season? Perhaps using snow/rain to refill??

A guide I copied years ago and worth keeping-

 

[Ron Stordahl]

As I mentioned we partially drain to winterize so as to avoid freezing pipes which would be very costly. In the spring we pump the remaining very dirty water out to do maintenance including painting if needed. Then we refill with city water, which has a pH just below 8 and no CYA.

My interest is if there is a balance between Tri-Chloro and Cal-Hypo which would be advantageous to limit CYA and make attaining a pH of 7.5 with less Soda Ash. I doubt if Calcium Hardness would be an issue for our brief season when the water is completely replaced each year.

 

[Mdragger88]

If you mean, is there a specific recipe that will work in your specific situation- yes, but only your testing will lead you there.
If you wish to continue use of the Trichlor pucks you will want to stop when cya reaches 40 or so then switch to a different chlorination method that doesn’t add cya such as cal hypo or liquid chlorine. If cya falls low go back to pucks for a minute.
Doing this will result in less acid being added to the water so ph rise will need to be controlled separately with Muriatic acid additions as needed. The flip side of the coin is that you likely won’t have an issue with ph/ta inadvertently going too low like with the pucks so soda ash, baking soda etc. will likely not be necessary. Also, trying to Keep ph at exactly 7.5 is not necessary. In the 7’s is fine. No need to get on the ph/ta merry go round for perfection’s sake.

Whichever chlorination method or combination of them you choose be sure to always follow the FC/CYA Levels to ensure you are keeping your pool sanitary. As cya increases so does the necessary minimum fc level needed to keep nasties at bay.
Disclaimer ** The mixture of cal hypo & Trichlor can cause an explosion so if you wish to use a feeder they must each have their own dedicated one. Aka - you can’t just add cal hypo pucks to a trichlor feeder or floater.
No two chlorine products should be allowed to mix so they must be stored separately in a way to ensure that doesn’t occur. Once they are thoroughly mixed in the water it is ok to add something else. Same goes with acid & chlorine.

You are dealing with quite a large pool with a short season so perhaps a liquid chlorine dosing system would be helpful if you are looking for something more hands off than manually dosing daily. In commercial situations a liquid chlorine dosing systems & an acid injection systems are quite common. There are also residential versions available with various levels of automation.

 

[mgtfp]

Quick research says Tri-Chloro's pH is 2.9, Cal-Hypo's ph is 11.8 (and without any CYA).

The pH-values of the materials themselves are not very telling, it's more about what the involved chemical reactions do. pH is only defined in watery solutions to start with, so to give a solid substance a pH is a bit delicate. There are definitions to assign a pH to solids by adding defined amounts of a solid to defined amounts of water, for comparability. But you can't just take the average of two pH-values and say the two substances cancel each other out. pH is a logarithmic scale, the correct math is a bit more complex.

When adding trichlor to water, the dissolution process is acidic, and pH of the pool water goes down. The chlorine usage reactions turning FC into salt (like chlorine getting deactivated by UV, or chlorine oxidizing things) are also acidic, so once the added FC has been used and the FC-level is back to where it was before the trichlor addition, pH goes down even further.

When adding cal-hypo, the dissolution reaction as basic, so pH goes up a bit. But this initial pH-rise is being compensated by the following acidic process of using the chlorine, so once the FC-level is back to where it was before the cal-hypo addition, pH will also be back to where it was before. In reality, it will be a bit higher than before, because of CO2 outgassing that happened in the meantime. The same applies to all hypochlorite sources of chlorine (and chlorination with an SWG), so pH-wise, liquid chlorine behaves the same as cal-hypo.

If reducing the CYA increase by sometimes using cal-hypo instead of trichlor makes sense in your situation, depends on parameters like your current pool-water CH and TA, the CH and TA of your fill water, how much rain fall you get over the year, how much water evaporates in summer.

The discussion should really start with posting a full set of your pool water parameters, and also the CH and TA of your fill water. Ideal would be to see the trend of your CH over a couple of seasons - being a TFP member since 2011 you surely have that.

I would recommend to use liquid chlorine for chlorination, and muriatic acid for pH-control. Muriatic acid is required to control the pH-rise by CO2-outgassing, which will no longer be (over-) compensated by trichlor. Once your TA is somewhere in the 50-80ppm region, you will likely never need to add baking or washing soda ever again, and your pH might be stable enough in the higher 7-range to only require occasional muriatic acid additions.

But whatever you do, take the Mdragger88's explosion warning serious.

 

[Toxophilite]

I played that with my pool, and with my pH balance requirements, I never knew whether I was coming or going. I finally just settled on one chlorination method, LC, and what would give me consistency so that I could relax and plan scheduled maintenance adds.