Starting resurfaced pool

[chem geek]

which also happens to be the max recommended by the National Swimming Pool Foundation CPO Handbook Water Chemistry Guidelines I saw page 44 in the little guide that came with my K2006C

The FC that is 5% of the CYA level works well for saltwater chlorine generator pools, but isn't high enough for non-salt pools dosed with chlorine such as bleach or chlorinating liquid, where the minimum FC is around 7.5% of the CYA level (this level is pretty consistent with Ben's Best Guess chart). I don't know if the higher salt levels are the reason or the more continuous dosing (I don't think that's it because peristaltic pumps seem to need the higher level). Also, these targets are for the worst case with plenty of algae nutrients, BUT the pool is still expected to have good circulation so that these minimums are maintained pretty much everywhere in the pool. And this isn't perfect, but seems to have a failure rate of less than 1 in 5000 pools which is pretty darn good. It also is for green and black algae -- yellow/mustard algae needs higher chlorine levels to prevent from growing so it's best to eradicate it if possible (or use other means such as a phosphate remover).

The maximum 4 ppm FC often quoted in the industry comes from the EPA drinking water limit. It doesn't make any sense for pools since 1) you aren't drinking the water (at least not 2 liters per day of it which is what the EPA assumes for their drinking water standard) and 2) with CYA in the water the active chlorine level is very low (not relevant for drinking, but relevant for oxidation rates of swimsuits, skin and hair). In fact, quite a few states ignore the EPA limit in their state codes for commercial/public pools. Florida has a 10 ppm FC maximum, Texas has an 8 ppm FC maximum and New York has a 5 ppm FC maximum all exceeding the EPA limit (New York also bans CYA in any commercial/public pools -- an over-reaction due to past Crypto outbreaks).

When figuring in comparative pricing, don't forget that with Trichlor you also had to add pH Up or Alkalinity Up to maintain pH and TA. When you factor that in, bleach or chlorinating liquid is not necessarily more expensive and in some places it's less. Also, you may be able to get chlorinating liquid for less -- your 2.2 cents per fluid ounce for what I presume to be 8.25% bleach is roughly equivalent to $4.27 per gallon for 12.5% chlorinating liquid. Mine costs around $3.95 per gallon though I just used a coupon today which was effectively for 25% off (1 gallon free when getting a case of 4 gallons). One gallon of 12.5% chlorinating liquid adds 12.5 ppm FC to 10,000 gallons (because the % is usually in Trade % which is a volume %, not weight %). It takes 18.24 ounces weight of Trichlor for the same amount of chlorine and to restore the TA (technically the carbonate alkalinity since the TA rises from increasing CYA) requires 13.8 ounces of pH Up (sodium carbonate or Arm & Hammer Super Washing Soda) assuming carbon dioxide outgassing raises the pH the rest of the way. As shown here, 25 pounds of Trichlor from a reasonably priced brand (GLB is usually one of the least expensive) is $91.14 so 18.24 ounces would be $4.16 just for the Trichlor. As shown here, 8 pounds of pH Up is $16.10 so 13.8 ounces would be $1.74. Even if you were to get the grocery store equivalent which is Arm & Hammer Super Washing Soda at Walmart for $3.24 for 55 ounces so 13.8 ounces would be $0.81. I don't see how your bleach is more expensive than Trichlor (unless it's only 6% and not 8.25%).

Since you mentioned the CPO Handbook, if you get that book or take the course I suggest you look at Certified Pool Operator (CPO) training -- What is not taught. The course and book are quite good, but there are some things that aren't stated and a very few that aren't quite right so that post fills in those details.

Finally, regarding the protozoan oocyst Cryptosporidium parvum, as Ben wrote it's easy to avoid by not having anyone with diarrhea use your pool. Also, with regard to CYA, it IS possible to super-chlorinate but it can be impractical when the CYA is high. To get the equivalent of 10 ppm FC with no CYA you need to raise the FC to roughly 10 ppm higher than the CYA level. Instead, it would be easier to just add some sodium chlorite to the pool to produce chlorine dioxide which can kill off the Crypto overnight in 12 hours. That shouldn't be necessary in residential pools, but would be an emergency remediation for commercial/public pools.