How To Maintain A Swimming Pool Part 3 (Adjusting Chemicals)

We'll start off with a mock reading as follows: In ground vinyl pool with a heater- Pool volume-20,000 gallons, Chlorine-0, pH-7.0, alkalinity-70, calcium hardness 120, cyanuric acid 20, iron-0.3, copper-0.1, phosphates-100 ppb (parts per billion). Before adjusting any chemicals, backwash the filter thoroughly and bypass any timers (I recommend running the pump/filter 24/7 whenever adding chemicals). Good circulation along with the right chemicals is vital to getting the pool back into shape.

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Based on these readings, I would start by adjusting the calcium level. The calcium level needs to be at least 200 ppm, but I want to increase it to at least 300 ppm. The reason I want to increase it to 300 ppm is because throughout the pool season evaporation, backwashing and "splash-out" will lower the calcium levels. This goes for all chemicals. By increasing it to 300 ppm (or even 400 ppm for that matter), the calcium level will still be within an acceptable range in the event I need to add fresh water to the pool. To calculate how much calcium hardness you will need, you simply subtract: (300-120= 180). I need to increase the calcium by 180 ppm. You will typically need 1 1/4 lbs of calcium chloride to increase the calcium level by 10 ppm in a 10,000 gallon pool. Multiply the 1 1/4 lbs by 2 (for 20,000 gallons) and you get 2.5 lbs needed to increase the calcium level by 10 ppm per 20,000 gallons. I will need this dose 18 times (10 ppm x 18= 180 ppm). 18 x 2.5 lbs = 45 lbs. Now that I know the amount I will need, I can start adjusting my level. Calcium chloride can be a harsh chemical if not handled properly. Do not add more than 10 lbs at a time per 10,000 gallons of water. For this pool, I will start by adding 15 lbs (20 would be o.k. since it's 20,000 gallons) and retest then add the second dose 12 hours later.

My next step would be to increase the alkalinity. I want to increase it to 100 ppm. To achieve this I need approximately 1.5 lbs per 10,000 gallons of water. Using the same calculations of above, I will need roughly 6 lbs. I'm going to wait until at least 24 hours have passed since I adjusted the calcium hardness otherwise the chemicals may react and cause the pool to turn cloudy. The 6 lbs can be added in one dose.

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Once I've given the alkalinity time to circulate in the pool, I'm going to re test the pH. The reason why is because the pH will increase slightly when you adjust the alkalinity. This time when I tested the pH the results were 7.2. It's within range so it won't need to be adjusted. (See step 6)

Next, I will add a metal remover before adjusting the chlorine. Chlorine reacts to metals in the water (green hair) so I want to remove any traces of metals before hand. I'll add one liter for my size pool and retest after 4-6 hours.

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Once I have my desired results, I will increase the cyanuric acid level. I'm using the liquid version since it will give me quicker results. One gallon per 10,000 gallons will increase the CYA to 32 ppm. Since I'm already at 20 ppm CYA, I'll add two gallons. After a few hours, I will retest and repeat if necessary. If you have a salt system, please follow the instructions in your owner's manual regarding the recommended cyanuric acid level.

Next I will focus on the chlorine. Shocking the pool should be done in the evening since the sun will burn it off (no cyanuric acid). Brushing the pool walls and floor before shocking will ensure any algae present in the water is killed by the shock. Slow dissolve chlorine tabs should be used at all times either in an automatic chlorinator or a chlorine floater. The exact amount will depend on a lot of factors. I recommend filling up the chlorine feeder or floater and adjusting the dosage amount as necessary. Back in step 4 I mentioned that I wasn't going to adjust the pH. The reason for this is because adding chlorine to pool water will typically increase the pH. Most types of chlorine will have a greater effect than others. After I shocked the pool, I tested the chlorine the next day and it was 7.4. If you have a salt system, please follow the instructions in your owner's manual regarding shocking and increasing the chlorine level.

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My last step is treating the phosphates. The reason why is that some chemicals contain phosphates. I'll need approximately one quart of a phosphate remover (amount will vary depending on the concentration of the product). Once I've added the dosage, I'll let the pump and filter run over night and re test all my levels in the morning.

After a re test, all my levels are within range and the pool looks crystal clear. Time to go for a swim.

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