Pump Run Time and Algae

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Pool Tool

Pool Tool

0
May 15, 2014
761
Western Chicago Area, IL
Hello all,

So I recently took a 5 day vacation and returned home to an algae bloom. I don't have the exact numbers in front of me, but I do at home. CYA was around 25 so I boosted the FC to shock levels (10-12 ppm) with liquid chlorine, filled the chlorinator with Trichlor and set pump run time from 10 am to 8 pm before leaving Monday evening. Wednesday afternoon, my BIL checked pool (10 ppm FC) and attempted to vacuum. Unfortunately a skimmer line leak complicated that but that is a different story. Since the FC was fine he left it as is. Fast forward to Saturday morning we arrived home to a green monster but measured FC still at 6.5 ppm ~ 12 noon.

The pool was covered with blue solar cover the entire duration short of the vacuum attempt. Skimmer line was off and plugged so main drain was the only pump inlet open. I have no data to certify that I didn't drop below the minimum FC during my time away, but assuming I generally only lose 2-4 ppm of FC on a normal day with the cover off and without pucks in the chlorinator, I have a hard time believing that I fell below the minimum.

I know no way to quantify, short of experimentation, just how much and how fast FC is added via my chlorinator. Additionally I cannot estimate normal FC usage during the day with the cover on blocking UV rays. But assuming that I was in a downward slide with FC from Day 1 foward (debatable), I know the chlorinator would not have added 4.5 ppm of FC from Sat. at 10 am until Sat. at noon when I tested it at 6.5 implying that I was not below the minimum.

While reading the "Determining Pump Run Time" article, the sentence "One thing to keep in mind is that pump run time does not prevent algae, only maintaining a proper chlorine level can do that." stuck out. Yes only free chlorine can prevent algae, but what part does circulation play? Assuming that the chlorine finds a happy medium and is evenly diffused throughout the pool, how oh how was there an algae bloom??

I have had several bouts with algae this year and being a first time pool owner I have learned many lessons along the way. I have read several articles on covers maybe or maybe not contributing to algae growth and that covers prohibit gases from venting, but I wanted to start a new thread for help.

Any ideas or comments would be welcome. Oh, since that time I have completed SLAM and levels are leveling out. All readings are with the trusty TF-100. I will post numbers in a few hours. Thanks.
 
Pool Tool said:
While reading the "Determining Pump Run Time" article, the sentence "One thing to keep in mind is that pump run time does not prevent algae, only maintaining a proper chlorine level can do that." stuck out. Yes only free chlorine can prevent algae, but what part does circulation play? Assuming that the chlorine finds a happy medium and is evenly diffused throughout the pool, how oh how was there an algae bloom??
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Because your FC was too low for your CYA level (despite the numbers you posted). In order for algae to grow, the FC level must be low enough. Run time should have very little effect on getting algae blooms as long as the FC level is sufficient (including UV extinction) to prevent algae from starting. However, if FC is not high enough and algae starts to grow in one part of the pool, then extra circulation will help keep the growth rate down. But that isn't really solving the problem. The problem isn't lack of circulation, the problem is low FC.
 
Sounds like your using pucks, and that will raise your CYA, which will require a higher FC level to be effective.

If you're have bouts with algae then your chlorine level is dropping below the recommended level based upon your CYA level.
http://www.troublefreepool.com/content/128-chlorine-cya-chart-slam-shock

The chlorine kills the nasties, the filter catches dead nasties, the pump moves the water.
 
I think that proper circulation is vital for maintaining an algae free pool. If in some places the water does not mix because it does move out of there, then it does not even get the sanitizing agent. Moreover, close to the wall surface the water moves slow even in areas with good circulation. Brushing the walls mix water very well and this you have to do in order to get faster a clean pool. For the best water circulation one should divide (if possible) the flow as follows: 1/3 one skimmer, 1/3 second skimmer, 1/3 main drain. Still all this would not work without the proper level of sanitation.
 
Very little run time is necessary to circulate and mix water in all parts of the pool and the study in my signature clearly shows this to be the case. Do you have a source for your claims?
 
You mentioned you put trichlor in the chlorinator. Is this an in-line chlorinator? Did the pucks dissolve? If not, this may be what happened - you put pucks in but the pump/water flow did not get the puck chlorine into the water. A floater may have been more effective if so.
 
Yes, it is an in-line. The pucks hadn't dissolved fully but partially - I had the chlorinator flow valve set at 2 with a max of 5. Started at 12ppm FC on Monday night, then brother in law measured 10 ppm FC on Wednesday afternoon and I tested 6.5 ppm FC Sat. afternoon.

I wonder if there was existing, but unseen algae present that would have been "controlled" by brushing when we were home that thrived under the cover while we were gone.
 
Pool Tool said:
I have had several bouts with algae this year and being a first time pool owner I have learned many lessons along the way. I have read several articles on covers maybe or maybe not contributing to algae growth and that covers prohibit gases from venting, but I wanted to start a new thread for help.
Click to expand...
Pool Tool said:
I wonder if there was existing, but unseen algae present that would have been "controlled" by brushing when we were home that thrived under the cover while we were gone.
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I think you are over thinking it. Did you ever SLAM completely until the end? If yes, great but at some point FC got below the minimum and let the monster come back. If no then the algae has always been there, just supressed by "just enough" chlorine to keep a full bloom from happening.

In either case the only solution now is a SLAM . Get a good current CYA number and SLAM away.
 
I agree with tim. Get some good numbers on your cya. That using a t100 test kit or another similar test then do a slam. If you complete the slam, stay with liquid chlorine and keep the levels high enough you shouldn't have algae problems at all.
 

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To answer mas985. There are many studies for the flow gradient of a liquid close to a smooth wall. Just found one: http://physics.stackexchange.com/questions/109395/why-arent-airplanes-like-golf-balls. Close to the wall the liquid speed is almost zero. Still small molecules can diffuse these small distances, but this physical process takes some time. In the study that you have mentioned all pools were functional and not defective, therefore a proper water circulation was present in all pools. In the Tool Pool case only the main drain intake was operational making possible a short pathway for water from the outlet(s) to the intake, leaving corners and other areas out of circulation and I can even quote from your own study: "Improperly adjusted eyeballs can cause a multitude of circulation problems". So I maintain my statement: Proper circulation is vital for maintaining an algae free pool.
 
I don't think anyone ever said that proper circulation wasn't necessary. I think where we may disagree is how much run time is required to get proper circulation. In the study, they showed that the pools did not show an increase in water quality after 2 hours of run time. Also, many on this forum, including myself, have found that very little run time is required for proper circulation and maintenance of a pool so there are many examples of this working in practice.

But even in the OP's case, proper aiming of the returns should be able to offer adequate circulation of the water independent of the suction ports used so I really don't that is the issue especially with 10 hours of run time. As the study correctly points out, running the pump 24/7 does not solve algae issues. Only adequate levels of FC can do that. The solution to the OPs problem is to raise FC levels, not pump run time.

[EDIT] I want to add that my comments above only apply to regular maintenance. During the SLAM process, run time/circulation is more important because the killing of algae consumes FC so that needs to be constantly replaced.
 
mas985 said:
I don't think anyone ever said that proper circulation wasn't necessary. I think where we may disagree is how much run time is required to get proper circulation. In the study, they showed that the pools did not show an increase in water quality after 2 hours of run time. Also, many on this forum, including myself, have found that very little run time is required for proper circulation and maintenance of a pool so there are many examples of this working in practice.

But even in the OP's case, proper aiming of the returns should be able to offer adequate circulation of the water independent of the suction ports used so I really don't that is the issue especially with 10 hours of run time. As the study correctly points out, running the pump 24/7 does not solve algae issues. Only adequate levels of FC can do that. The solution to the OPs problem is to raise FC levels, not pump run time.
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:goodpost:
 
Thanks to all for the posts. During my vacation, I don't believe my FC was near the minimum let alone below it so that is why I was asking about the circulation / cover issues. More to gain knowledge than anything. With having limited knowledge, I generally try to simplify the conditions but as we all know pools are a little more complex than that. Like always, after reading the posts there is always more to learn and I will be a little better prepared next time. One common theme is FC prohibits algae and I can easily manage FC, so that is the plan forward.

Good thing, the pool is almost completely clear now and I am hoping to do OCLT over the weekend. I also will be pulling the light and stairs tonight and give all the toys a good bleach bath. I will play close attention as FC drifts down (after OCLT) to see if and when there is any return sign of issues. Thanks again.
 
The minimum/target FC levels are a guide not absolutes. If you are still developing algae at recommended levels, then you probably need higher levels. But I suspect the problem was that you didn't fully kill the previous algae breakout. Also, some forms of algae (e.g. Mustard) require much higher levels of FC for complete kill. Also, make sure you brush the sides of the pool while the FC is high.
 
Weekend update: Friday night took FC to mustard shock levels as water was pretty much clear. Brushed a few times and ran pump constant.

Sat. afternoon "dirt" gathered near junction of walls and floor. I jumped in the pool to inspect and realized it was actually algae growing. Stayed in for a few more minutes to remove the light and scrub around the fiberglass steps then brushed the pool by hand. Majority had a very thin layer of green dust when brushing. Got out of pool, rinsed off and re-brushed pool again. Removed the drop in steps and found a serious case of algae living inside. So I tore down the steps, doused with bleach and left out until Sunday.

Sunday held a unsuccessful attempt at OCLT, 2 ppm loss, which was expected since I could see algae growing on Saturday. I let FC levels to drop normal shock levels and plan to keep a closer eye on the algae growth. Ran pump and brushed frequently.

I had seen this algae accumulate before but always thought it was dirt. The pool is surrounded by several trees, which are always dropping something whether pollen, leaves and now acorns, and assumed they were causing the dirt. This was the first time I actually got in to inspect it closely. It was a dark green, generally I hear mustard algae looks more yellow green?

So my path forward is to continue SLAM and wait for clear water and no visible algae then jump to MA levels for 24 hours. Question, if I saw this growth while FC was around 20; should I maintain a MA level for an extended time, or maintain normal shock? Current CYA = 30. I know recommended MA level is only suggested for 24 hours after a successful SLAM so I might be jumping the gun, but I have also read posts of extended MA levels being required to eradicate all MA. Thanks to all for reading and any suggestions.
 
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