Algae in a salt system pool

[Chris]

Algae has been recurring up in my neighbors salt water pool for about two weeks. All the levels seem to be in the correct range as per my pool store that tested the water and my test kit. Is it ok to add shock to kill it immediately? Why is this happening and what do I do?

[mas985]

First, it is fine to shock right away. This will not have any affect on the SWG.

Second, for a SWG, chlorine levels should be about 5% of the CYA level so if the CYA is in the 60-80 ppm range as most manufactures suggest, then chlorine should be in the 3-4 ppm range. Unfortunately, most manufactures will recommend 1-3 ppm for chlorine which is fine for bacteria control but can open the door for algae blooms. BTW, what were the actual test results?

[Blazing]

First off, the question is, is the algae in the water or is the algae only on the walls. Keep in mind that the chlorine in your water, whether from tabs or from a chlorine generator (Salt System) is a lousy algaecide but a good sanitizer. Those are two different things. Next, the previous post is correct. I live in Phoenix, and if I do not maintain a FREE Chlorine reading of 3.0 I am in danger of having pools turn green. Also, if your pH ,s maintained below 7.6 you will also have a problem as all plants, which include algae, thrive in a low pH low alkaline invironment. I have pools with a Chlorine reading so high that the health department would close the pool for that reason, that have had excelent circulation and filtration, turn green and when the pH was raised, the problem went away without changing anything else.

That said, I offer free solutions to almost all pool problems on my web site solvemypool. There may be issues covered there that will assist you in solving your current problem. Check out solvemypool and the sections on water chemistry, algae on pool surfaces, and green and cloudy water as they are quite thorough, and should eliminate all, or at least most, of the issues you will face. Free is good.

[chem geek]

Keep in mind that the chlorine in your water, whether from tabs or from a chlorine generator (Salt System) is a lousy algaecide but a good sanitizer. Those are two different things.

Chlorine is NOT a lousy algaecide. It only seems that way because most in the pool industry do not understand the chlorine/CYA relationship (definitively determined in 1974 in this paper. Chlorine alone can prevent algae growth if the FC level is high enough relative to the CYA level. This is demonstrated in tens of thousands of pools on The PoolForum and Trouble Free Pool including hundreds and thousands of pools serviced by professionals also reporting on these sites.

The pool store in my area has a pool service that services over 1000 pools (they've got lots of trucks and personnel) and I've talked to the manager who says they find that they cannot have the CYA be much above 100 ppm without getting too many algae problems (but they don't try maintaining a higher FC level as the CYA level gets higher). They generally keep the Free Chlorine (FC) level targeted at 4-5 ppm which prevents algae growth. Because they service the pool only once a week, they use Trichlor pucks to maintain the chlorine level, but this increases the CYA over time so regular water dilution is needed. Fortunately we get winter rains so that the pools get nearly 50% dilution each winter, but those with cartridge filters often need more manual dilution to keep the CYA lower. The CH in the fill water is only 50 ppm so that is not a problem and the evaporation rates aren't as high as in Arizona.

One does not have to maintain a pool this way and can instead use unstabilized chlorine to prevent the rise in CYA and not need to dilute the water is much or as often.

Also, if your pH ,s maintained below 7.6 you will also have a problem as all plants, which include algae, thrive in a low pH low alkaline invironment. I have pools with a Chlorine reading so high that the health department would close the pool for that reason, that have had excelent circulation and filtration, turn green and when the pH was raised, the problem went away without changing anything else.

Algae growth is somewhat faster as the pH gets closer to 7.0, but it doesn't explode in such growth. Algae growth drops off precipitously as the pH approaches 9 but that's obviously too high to maintain. We've seen plenty of pools on multiple pool forums with algae prevented using chlorine alone even when such pools had lower pH, mostly to prevent metal staining from earlier use of copper-based algaecides or from earlier use of metal ion (copper/silver) systems.

See this post I wrote in response to another one you wrote in a different thread for more info. Another alternative source for how to maintain a pool is found in the Pool School.

[karla]

My husband and I travel for work most of the time. We were home two weeks ago to find our pool water looking green. I took in a water sample and was given instructions for mustard algae. We added 12oz of Shock & Clear and then 4 lbs. of shock granules. The next AM I cleaned and backwashed the pool and added 4 lbs. of shock. I repeated the process again the next AM. The water was very clear by the 4th day. I then took a sample in and added salt and chemicals per their instruction. We left on the 5th day to go back out of town. I have a college age son who is in and out of our house and had him check salt level and let me know how the water looked each time he stopped by. Yesterday he was at the house and called to tell me the water looked green again. I am going to be gone another two weeks. My first question is will it make my situation worse if I don't do anything until I get back and can be there to monitor the process? My second questions is did I not get rid of it the first time and what should I do now? I appreciate any help you can give me.
Thanks,
Karla
Rincon, GA

[morgus]

I have a salt pool that had a terrible algae problem. No amount of shock could clear it. It turns out I had a high amount of phosphate in the pool that the algae was thriving on. One bottle of PhosFree took care of it. Pool stores can test for phosphate if requested.