The answer partly depends on the chlorine usage in the pool. If you know the typical chlorine usage (you can give it as number of pucks per week, etc., if you know the weight or size of the pucks) then you can see how much bleach you would need to add (I give generic numbers below for 1 ppm FC). If you do not know chlorine usage, then you can answer the following questions to help estimate it. Is the pool open to direct sunlight? Is it ever covered and if so when and with what kind of cover (opaque or clear for solar)? What is the typical bather load -- how many bather-hours per day? What is the typical use of the pool -- is it light wading or heavy competitive swimming (I suspect mostly splashing and wading with some swimmers). What temperature is the pool kept at?
To add just 1 ppm FC to this size of pool requires 1.4 gallons of 12.5% chlorinating liquid or 2.8 gallons of 6% bleach or 2.3 pounds (about 4.2 cups) of 65% Cal-Hypo or 1.6 pounds (3.2 3" 8-ounce tablets) of Trichlor.
This size of pool could use an automated chlorination system, whether it be SWG or chlorinating liquid injector or Trichlor puck feeder. Of course with Trichlor, you have to be careful about CYA rising too much. What kind of filter does the pool have and if it's D.E. or sand, what volume of water is backwashed how frequently? You might be able to use Trichlor exclusively if you dilute the water frequently enough to keep the CYA in check and you could keep the TA high to have the outgassing of carbon dioxide balance the acidity of the Trichlor (so you would just be adding Sodium Carbonate / Soda Ash / Washing Soda and sometimes Sodium Bicarbonate / Baking Soda every now and then to maintain the TA and pH. Of course that wastes a lot of water, but if you already have a D.E. filter that might be the best option. If CYA levels rise too quickly, then alternating with granular Cal-Hypo can be done for a while, but then calcium will eventually rise. Without sufficient dilution (either regularly or in an annual drain/fill adjustment), neither Trichlor nor Cal-Hypo can be used as the only chlorine sources.
Richard
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