Have you ever removed the cover in the spring, or come back from a vacation only to discover a green swamp where your pool used to be? Getting algae, and having to defeat it, is a chore that even the most experienced of us have had to face at some point. Fear not; with proper preparation you can turn your pool back into that sparkling oasis you remember.
This post is for those of you that have a serious green algae problem; murky, green water that has been that way for days (or months or years!) in an outdoor pool. While many of the same principles apply to other kinds of algae, we are going to address the nastiest of algae filled pools here.
There are two major “phases” to understand about getting rid of algae. First, algae is a plant and it is constantly growing. If you stop the process before it is completely killed, it will bounce right back, and all the time, money and chemicals you invested will be wasted. Think of fighting algae as a race-you need to kill the algae faster than it is able to grow back. If you give algae a few hours without chlorine, it will be come back and you will loose ground.
Second, the amount of chlorine you will need depends on the CYA level. The higher the CYA level, the more free chlorine it is going to take. If you do not have an accurate read on your CYA level, you risk either not using enough chlorine, failing to get rid of the algae, using too much chlorine and possibly causing corrosion in metal parts, or shortening the life of your liner. None of these are the result you are looking for!
Like most projects, there are several things you need to have in place before you start. Most importantly, the pump and filter need to be working. You will need to have the pump running 24/7 during the process to make sure the chlorine is circulated efficiently or you might not get all of the algae. Make sure you know how to clean and/or backwash the filter, as well as what the filter pressure reading is when the filter is clean.
Next, you need to know where your CYA level is. Having this information is critical in determining the correct amount of chlorine you will need to create the proper kill environment.
If you have murky pool water, this will cause the standard turbidity test (the test where the black dot disappears) to read higher. A nifty trick to partially compensate for this is to filter the water sample through a coffee filter before you test it. If the water is cold, it is also best to allow it to warm up to room temperature before testing CYA. If you are unable to accurately test CYA, you can have it tested at most pool stores. In any event, don’t depend on a CYA test that is done when you have algae. While it is acceptable for what you need to do to get rid of the algae, it should be re-tested again after the algae is gone.
Please understand that it is very important that the CYA level not be zero. If the CYA level is too low, you run the risk of losing too much chlorine to sunlight and the algae will be able to get ahead of you. If you find that your CYA level is below 20 ppm, you should add at least 20 ppm of CYA/stabilizer in a sock in the skimmer (you can also use di-chlor if you have some on hand and know ow to properly handle it). Do not pour the CYA directly into your skimmer, since you will be cleaning/back-washing the filter and any undissolved CYA will just be wasted (remember, it can take CYA up to a week to completely dissolve). Don’t forget to re-test your CYA and adjust as needed once the algae is gone.
Having too high of a CYA level is also problematic. If your CYA is too high, cleaning up the pool will take much higher levels of chlorine. If a reliable test shows that your CYA level is above 90 ppm, you should replace water (or have a Reverse Osmosis treatment performed) to bring the CYA level down to 90 or lower before continuing.
Once you know your CYA level you can look up the corresponding FC shock level (use The Pool Calculator to do this). Enter your CYA level in the “NOW” column on the left and then look at the blue Suggested FC Levels section towards the bottom. This will tell you where you need to be, and how much chlorine, in each concentration, to add to your pool.
Next, you will want to have a FAS-DPD chlorine test kit. The FAS-DPD test is able to measure FC and CC up to very high levels. You need that in order to really know where your FC level is, as you are just guessing without this information. The Taylor K-2006C kit contains the FAS-DPD chlorine test. Taylor also sells the FAS-DPD test separately (you can purchase it here if you do not have it: http://pstpoolsupplies.com/taylor-te…er-r-0870.aspx). While not impossible to fight algae without this test, it involves a lot of guess work and extra chlorine.
Before you get started, make sure that you have enough chlorine on hand so that you don’t end up running out to the store to buy more every half hour! We strongly suggest bleach, but cal-hypo, di-chlor, and lith-hypo can all be used, although with some down sides. You will be using a lot of chlorine, so the negatives of bleach options can be quite significant! At a minimum, it would be best to have four times the amount of whichever product you have chosen to bring your pool to shock level available. The longer it has been since the pool was clear means the more chlorine you will need, so be prepared. Use The Pool Calculator to calculate the amount that you will need to achieve the proper shock level for your pool.
Adjust the pH level between 7.2 and 7.4 before you start. As the pH test is not reliable at high FC levels, and since pH typically goes up, start off a little on the low side. Because the FC level is going to be high for several days, you need to get the pH right before you start.
If your pool has been sitting unattended and/or uncovered for longer than one winter, you should always pull everything solid that you can out of the water before shocking. Use a skimmer net on a pole or your pool brush, and you should be able to fish out most of what is in the water. Work slowly and you should be able to get a good portion of the debris out, even without being able to see it.
If you have issues with metals, have recently used a copper based algaecide or regularly use a ionizer/mineral system, you will need to take additional care to avoid metal staining. While you are shocking the pool the pH will temporarily go up more than it usually does, and can cause any metals in the water to deposit as a stain the pool surface. If you are concerned that there may be problems with metals, you should lower the pH down as close to 7.0 as you can before starting and add some sequestrate to prevent metal staining.
If you have a SWCG, tab feeder or Liquidator, you will still need to use another chlorine source for killing off the algae, as none of these devices can produce high enough FC to shock. All of these devices are designed to add chlorine slowly and steadily over many hours; not to create the dosage needed to kill algae. To quickly kill algae, you need to put lots of chlorine in all at once. A SWCG, tab feeder or LQ can be very helpful in the follow up stages to maintain shock level, but for the initial couple of chlorine applications you will need to use another method of introducing chlorine to your pool.
Begin your algae killing efforts when you have as much time as possible-preferably several hours in a row-to work on your pool. You will also need enough time to follow up at least twice a day for the next several days. The more time you can spend, the quicker the process will go. Set the pump timer/pool automation system to run the pump continuously for as long as it takes until the water is completely clear. You are now ready to start killing the algae.
Start by adding enough chlorine to bring the pool up to shock level. Wait half an hour and then test the FC level, adding enough chlorine to bring the FC back up to shock level. Repeat the cycle of testing, adding chlorine and waiting as many times as you have time for, or until the FC level remains nearly at shock level after one hour has passed.
The first time through the cycle you can safely assume that the FC level starts at zero, and after that you will want to test the FC level, adding only as much chlorine as needed to bring it back up to shock level. You will find The Pool Calculator is very handy for this since you can enter your pool size, the test result in the NOW column and shock level in the GOAL column, and it will tell you how much bleach you will need to add.
The first few times the FC level is likely to be zero. Once the FC level starts to degrade slower and stays closer to shock levels, you can extend the length of time between tests. The key is to get the FC level to stay as close to shock level for as long of time as possible to kill the algae.
If you don’t have a test kit that can reliably measure high FC levels, you will need to do some guessing. One indicator that you can use is the color of the water. As long as the water remains dark green, wait one hour and then assume that FC is zero. You will notice that the algae will start turning gray or white when the FC level starts holding.
Once the green color starts to fade you should brush the entire pool, taking extra care to get “hidden” areas around steps or ladders. Algae can survive high chlorine levels if it has been allowed to form a bio film on a surface. By brushing you disrupt the bio film, exposing the algae to the chlorine. Keep brushing at least once a day until the algae is all dead.
After several cycles, you will notice the FC level will be falling only slightly after an hour’s wait. At this point you can bring the pool back up to shock level one last time, and then move on to the follow up stage. Iif you are doing this in the morning and your CYA level is below 60, you should check the FC level one more time in the mid afternoon and bring it back up to shock level if it is needed.
In order to make sure that you got all of the algae, it is important to maintain the pool at shock level until testing shows that all of the algae is gone. Continue testing the water at least twice a day in the morning and evening and bringing it back up to shock level if needed. Do not stop brushing if there is even the slightest hint of algae left in the pool. By continuing to brush and maintain high FC levels, you will defeat this.
To be certain that you got all of the algae, measure the FC level after sunset and then again in the morning, before sunlight hits the pool. If the FC remained stable (within 0.5 ppm of the same reading overnight), and the CC level is 0.5 ppm or lower, then you have completed the kill. If you do not have a good test kit, you should maintain shock level until the water is completely clear and sparkling.
Once most of the algae is dead the water will turn milky or gray instead of green. That does not mean that you are done, and it can still take the filter up to a week to clear the water from this point (A DE filter can often do it in a couple of days, if you backwash it frequently enough). During this time, you should keep an eye on the filter pressure and backwash/clean the filter any time the pressure goes up by 8-10 PSI. DE filters will often need to be back-washed a couple of times a day for the first day or two, whereas sand and cartridge filters will usually last a couple of days between cleanings. If in doubt, clean/backwash the filter more often rather than risk letting it get clogged up and ineffective.
Getting algae is never fun, and it is sometimes unavoidable, as every pool and every situation is a little different. If you have questions, or things don’t exactly go as described, feel free to start a new topic describing your particular challenges. Once properly prepared, you can have the pool cleaned up in under a week. We bet you will do your best to avoid having to fight this battle again anytime soon!