Unexplained FC Consumption - it's back again

[toofast]

You can find out the chemical reactivity for thousands of common hazardous chemicals using the NOAA Chemical Reactivity Worksheet. However, that is referring to concentrated chemicals and tends to be very conservative (they even consider mixing water with sodium hypochlorite to be hazardous).

In general, the reaction of chlorine with alcohols is very slow, but it's faster for a secondary alcohol which is the case with propylene glycol (it has both a primary and a secondary alcohol). Hypochlorous acid may react with propylene glycol to form hydroxyacetone which then further reacts more quickly with chlorine to form glycolic acid and chloroform. This reaction will occur more quickly in acidic conditions so if you want to speed things up you might consider lowering the pH.

How much anti-freeze was used and was it 40% propylene glycol with 60% water? If you tell me that, then I can estimate how much chlorine it will take in total to get rid of the anti-freeze though in practice you just have to get through this unless you dilute with fresh water.

This is what I used, and perhaps 10 gallons in total

Product Description


West Marine Pure Oceans -50° (-46°C) Marine Antifreeze provides the ultimate in cold weather and corrosion protection for drinking water systems and all engines. Its premium additive package prevents corrosion of aluminum, copper, brass and solder, but will not harm rubber, seals or hose materials. The 3X-died bright pink color provides excellent blow-through visibility. Formulated with non-toxic, virgin Propylene Glycol (30% Blend), it is tasteless and contains no alcohol. This product is ready-to-use; do not dilute it.
•Provides burst protection to -50°F (-46°C) and freeze protection within a range of +12°F to +16°F (-11°C to -9°C)
•When testing with a refractometer or hydrometer designed for use with propylene glycol, freeze point readings on the PG scale will range from +12°F to +16°F

Note: The burst point of PVC pipes used in most drinking water systems is about -10°F (-23°C). When winterizing water systems in regions where temperatures can fall below -10°F (-23°C), we recommend using West Marine Pure Oceans -100°F (-73°C) Marine Antifreeze

 

[chem geek]

So let's figure out worst case which is 10 gallons of 30% propylene glycol in 14,750 gallons. Since the density of propylene glycol is roughly the same as water, this is (37.8541 liters) * (1000 g/liter) * 0.30 / (76.09 g/mole) = 149 moles. It takes one chlorine to convert propylene glycol to hydroxyacetone and three more to produce glycolic acid and chloroform so that's four total or 597 moles. In terms of ppm FC this is (597 moles) * (70.906 g/mole) * (1000 mg/g) / (55835 liters) = 758 ppm FC. [ Another simpler way of calculating this is from 0.3 * (10/14750) * 4 * (70.906/76.09) * 1,000,000 = 758 ]

That's a heck of a lot of chlorine so if in fact all that propylene glycol got into your pool and would react over time with chlorine then it looks like it would be worth doing significant drain/refill to dilute the propylene glycol out of the water. It's not just that it would take huge amounts of chlorine, but you could produce as much as 319 mg/L (ppm) of chloroform. As I noted in this post, " the 95% confidence level for lifetime excess cancer risk for continuously exposed human populations is 2200 ppb in air and 13,100 ppb in water." So the 319 ppm of possible chloroform well exceeds the 13 ppm for likelihood of starting to see increased cancer risk and that is due to toxicity (i.e. it's not mutagenic at low concentrations). Personally, I wouldn't take that risk and would seriously consider a drain/refill of the pool water.

I've started a new thread Antifreeze and Chlorine in The Deep End on this issue.

One thing you could do is have your water tested for chloroform which would be part of standard TTHM water quality testing, but when I've had that done for my own pool it wasn't cheap (around $130). You could see if it's already high and test again after a month to see if it increased substantially. If it's low (generally it's in the 50-200 ppb range so well less than 1 ppm) then your only consideration would be the higher chlorine demand and it's possible the cause for that is something other than the propylene glycol anti-freeze.

 

[mr_gunite]

So RV antifreeze isn't exactly non-toxic when used in a swimming pool year after year.

 

[chem geek]

To be determined. At this point it appears that it may contribute to additional chlorine demand, but we don't know what else may contribute to that happening (because it has happened in some pools but not all that use such anti-freeze that let it get into the pool water). Whether it actually produces disinfection by-products that are a problem has yet to be proven -- we should know after some water tests.

 

[S1ngram]

Oh no! Sorry to see you're back with the same problem as last year. My pool has been doing fine so far in terms of FC consumption this year. I really think my problem last year was related to residual chemicals (herbicides or fungicides) that may have been present in one of the hoses used to fill my pool.

Thank goodness you have found a culprit this time - it seems that way anyway. I'll be following you again to see how things go and offer moral support when I can.

There are so many things we can unintentionally introduce to our pools. Sometimes we're just a bunch of guinea pigs to help others find the answers to their problems later on.

 

[aussieta]

good to finally see a possible cause that matches the symptoms
if this turns out to be the cause maybe use a shop vac or similar to drain lines when you open the pool

 

[toofast]

So in reviewing all my dosing and charting...my CC has been at nearly .5 for about 30 days...never thought anything about it, till I reviewed last years numbers.

My CC finally is at 0 again tonight.

My FC consumption was/is still a bit high compared to what I think is normal....but I will continue to monitor....maybe I've turned the corner again. I did open WAY early this year vs. last year....wonder if the cool temps somehow helped.