As a pool owner, you may have experienced this before. You step outside, ready to swim, and your pool is cloudy and slightly green. What happened? Maybe you went a few days without testing? Maybe you had a huge party the day before with dozens of swimmers. Really, the gist is that you have an algae bloom due to lack of chlorine in the pool. ANd what happens to most people is that they end up in the pool store and get told that they need to buy Chlorine shock (usually Cal-Hypo), Algaecide and something to remove Phosphates. You bring it home after spending way too much money, pour it all in, and it seems to work, but slowly, and then a week or a month later you are back at the same problem.
If you have alage in your pool and you need to fix it right, the best way is to SLAM your pool. SLAM stands for Shock, Level And Maintain. Pool Logger has a built in SLAM mode to help you. Basically what you want to do is, instead of buying hundreds of dollars of useless chemicals that add more unwanted stuff into your pool. Go to the store and buy regular old bleach. Not the splashless and scented kind of laundry, but regular germicidal bleach. It usually comes in 121 oz jugs in 8.25% strength at your local grocery store or hardware store for around $2.50 a gallon. This is really all you need to clear up your pool, unless there are other issues like high levels of Cyanuric Acid.
First, you will need to test your CYA (Cyanuric Acid) levels and PH. PH testing is unreliable at free chlorine levels over 10ppm so you need to first get your PH to 7.2 -7.5 and then get ready to add the bleach. How much you will add depends on what your CYA levels are. If you have a CYA of over 100, then you may want to consider draining some water to get to reasonable CYA levels. Enter your full test results in Pool Logger. Make sure you pump is set to run 24/7 which SLAMing. Enable SLAM mode in the settings page. Now you are ready. You can click on the FC number on the Home Page of Pool Logger and it will tell you how much bleach to add and what your FC level should be at. (Make sure the % strength of the bleach is in your settings also) Now it is time add the bleach, pour it in slowly in front of a return so it distributes evenly. Wait 15 minutes and test to make sure you are at SLAM level, and if not, add what Pool Logger tells you to add.
So now you have shocked the pool. This is the first step in the SLAM. But now comes the hard part. You need to maintain shock levels until 3 things happen.
1.) Your pool water is crystal clear 2.) Your CC (combined chlorine) is 0.5 or less 3.) You pass an overnight chlorine loss test (more on this in a second)
All three of these things need to be true in order to make sure that no more algae is in the pool. Remember, you have to maintain these high levels of chlorine for days until you pass the tests. This means testing and then adding bleach or liquid chlorine multiple times per day.
During the SLAM you will need to do several things: You will need to test the FC often. You may need extra reagent if your CYA is pretty high as you will be using a lot of drops. You need to brush the pool at least daily, or as much as you want. Algae hates being brushed! And, Since algae is very good at clogging a pool filter, you may have to backwash your filter often in the beginning as alage is being killed. If it is clogging too fast for you to keep up, then set your filter on bypass at first and vaccum all the dead algae to waste before recirculating through your filter.
So, you are coming along fine and the water is really nice and blue and clearing up. Your CC's are 0.5 or less. It maybe time to try the final test. The OCLT, or overnight chlorine loss test. Basically, when chlorine is doing its job and you have nothing funky growing in your pool, you should not lose more than 1 ppm of chlorine at night because sunlight is the other thing that consumes FC. So what you want to do is wait until the sun goes down, test your FC. Record that number in Pool Logger. The next morning, wake up and test the FC again before sunrise and see if you lost more than 1ppm of chlorine. If you did, you aren't done, keep at it. If you lost 1ppm or less, and the water is clear and you have no CC's, you are done and now you can let your chlorine levels come down to target levels in Pool Logger. Don't forget to disable SLAM mode. Congrats!!
Now, don't let you FC dip below the minimum levels recommended by Pool Logger and you will not have to do that again!