Doing a "Bucket Test" for Chlorine Demand
In a perfect world, you'd always know everything you need to know about your pool. And, you'd know when you added a pool chemical exactly what it would do.
But, this is not a perfect world, so it's often better to experiment with a little water, rather than a whole pool full. In water treatment plants that supply potable water, or treat sewage, chemical doses and other treatments are tested using "jar testing", using special large glass jars and mixers.
"Bucket tests" for pools can be done for 5 reasons:
All bucket tests start the same way: with a bucket! White 5 gallon buckets like these from Lowes or this 10-pack from Home Depot are ideal.
- Chlorine demand testing. Often when pools have problems, it's hard to tell 'how much more chlorine' it will take to fix things. In particular, this is true when a pool is all slimed up with algae or bacterially generated ammonia. A chlorine demand bucket test can answer the question, how much chlorine will it take, to clean up my pool.
- Leak testing. Pools that are in use lose water for 3 reasons: evaporation, swimmer splashout, and leaks. Especially in dry climates, it's hard to tell how much water is being lost to evaporation. One form of bucket testing can answer the question: "Is it a leak, or is it evaporation?"
- Metals testing. Metals stain pools. Swimming pool water can get metals in it from many sources: algaecides, corroding heaters or pool parts, well water, water delivered by trucks, and so on. The problem is, many metal treatments HIDE the metals: they are STILL in the water, but they aren't showing up. Most tests for metals can't reliably detect sequested or chelated metals. But, a metals bucket test can answer the question, "Are there still metals in my pool water? What kind?"
- Floc testing. Many pools suffer from the big pump / little filter problem. This isn't so bad, when all is well, but when their pool is cloudy from dead algae, or precipitated calcium, or added phosphate remover, it can be very hard to clean up. And, it can be hard to tell what will help. A floc bucket test can answer the question, "Will this floc help my pool, or mess it up worse?".
- Lime softening. Calcium levels (hardness) can get too high in pools. One way to lower hardness is to drain the pool and refill with softer water. But, this not only wastes water, it can destroy liner or fiberglass pools. Lime softening is a way of removing calcium, by adding soda ash, till the calcium in your pool clouds the pool or drops out, and then can be filtered or vacuumed out.
You can get these at Amazon, but they are expensive there, so it makes sense to buy them locally, unless you are not near a large hardware or building suppy store. Used 5 gallon white pool chemical buckets are ideal -- if they are clean, and if you have any. A white mid-size trash can will work, too. But it HAS to be clean.
Otherwise each of the 5 bucket tests has different requirements.
When testing for chlorine demand, you'll need the following:
- A white 5 gallon buckets.
- A 1 gallon or 1/2 gallon clean milk jug or orange juice container (to measure with).
- A FAS-DPD chlorine testkit - either the K-2006 or the K-1515. (Test kit info page
- An OTO testkit, like the Taylor 1000 or the HTH 6-way drops kit. (Test kit info page)
- A *fresh* jug (96 oz or 1 gallon) of plain 6% household bleach.
- 4. A box of 20 Mule Team borax.
- 5. Lids or towels you can use to cover the buckets.
- 6. A plastic or stainless steel teaspoon & a tablespoon measure
- 7. A clean household long-handled stainless or plastic cooking spoon
To carry out the test:
- Use the gallon or half gallon measure to collect pool water.
- Fill the first white bucket with 4 gallons of POOL water.
(Measure by adding 4 measured gallons OR by adding 33 lbs of water to the buckets).
- Add 1 tablespoon of borax & mix -- test pH; it should be 7.6 or higher. Repeat as needed.
- Add 1 TEAspoon of bleach, and mix. Cover & wait 1 hour
- Test chlorine with an OTO kit. If the result is 5.0 or less, repeat the chlorine dose. (Keep track of how many teaspoons you add, in total)
- Once you have an ORANGE result, cover and wait 4 - 24 hours.
- Mix, and test the water for BOTH FC & CC with an FAS-DPD test.
- If CC > FC, add another dose of chlorine.
- Wait 4 - 24 hours, and repeat till FC > CC.
- Wait 24 hours & retest.
- If FC is less than 5 ppm, or CC > FC, add another dose. Continue as needed.
- Once FC > 10 ppm will hold for 24 hours , and CC < 2 ppm, you are ready to move to treating your pool.
Treating your pool.
- Each teaspoon = about 20 ppm, so if it takes 5 teaspoons to read the final step, your pool needs at least 100 ppm of chlorine.
- Calculate (or ask for) a 20 ppm dose for your pool, using whatever form of chlorine you have.
- Dose your pool.
- - Turn the pump on 24/7
- - Put your filter on "RECIRCULATE" or remove the cartridge.
(If your DE filter has no multiport valve, CLEAN your filter and add new DE.)
- - If you have a concrete pool, you may add the entire dose at one time, up to 100 ppm.
- - If you have ANY other form of pool, your dose limit depends on stabilizer level; CYA < 20 ppm, add only 20 ppm per dose; CYA > greater than 20 ppm, you can add 40 ppm per dose.
- - When you repeat doses, do NOT let your TOTAL chlorine go higher than your maximum: 20 ppm with CYA < 20 ppm; 40 ppm > 20 ppm.
"Chlorine demand" can be caused by many things. Severe, fast acting, chlorine demand is most often caused by ammonia left over form the degradation of cyanuric acid (stabilizer) by bacteria. This can occur if the pool is 'slimed' for an extended period of time. Slower acting causes can be dead algae, cheap algaecides, and more.
"Chlorine demand" does NOT refer to chlorine loss during the day. If you can hold chlorine levels OVERNIGHT, but lose chlorine rapidly during the day, this test is NOT for you. You have other problems, usually either a lack of stabilizer OR a prior use of bromine or sodium bromide algaecidal products.
If you do have a high chlorine demand, this test allows you to determine -- approximately, NOT exactly! -- how much chlorine it will take to get your pool to the 'finish' line. It will also allow you to distinguish fast acting 'chlorine demand' (ammonia?) from slow acting chlorine demand (dead algae that needs to be removed; a filter that needs to be cleaned.).
Dose ratio calc for teaspoon 6% bleach per 4 gallons:
0.52 lbs/cup x 1cup/48teaspoons => 0.0108 lbs bleach
0.0108 lbs bleach x 0.06 (%bleach) => 0.0065 lbs/Cl2
4 gal x 8.33 lb/gal = 33 lbs
(0.0065 / 33) x 1,000,000 = ~20 ppm Cl2