How fast can algae take over?

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T

TreeFiter

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In The Industry
Jul 2, 2012
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Saugerties, NY
Recently I was at a brand new pool. It had been filled the day before I serviced it. The water was trucked in from an underground lake. The water chemistry was pretty good. pH, TA, CH, CYA, and salt levels were all properly adjusted. I was there to do the first vacuuming so the pool looked perfect for the customer when they got home. I found that the chemistry was all in good shape with the exception of the chlorine levels. Both FC and TC were reading 0. The salt system was set at 50%. I turned the salt system up to 70% and shocked the pool. My thinking was that since it is the beginning of august and we have been experiencing weather in the high 80s for the past month, and the forcast shows the same for weeks to come, I needed to get chlorine in the pool quickly before algae took over.

My boss, on the other hand, didn't agree. He said I shouldn't have shocked it. I should have let the salt system bring up the chlorine on its own.

So I'm wondering if anybody has any information on how rapidly algae can grow in a pool with no chlorine. Is there a way to calculate how much algae will grow, or maybe find the tipping point where there is enough algae that it will begin to consume chlorine faster than it can be produced? Is there a way to calculate chlorine demand based on how long algae is allowed to grow?
 
I would have gone an intermediate route, bringing up the FC level manually to normal levels and letting the SWG take over from there. It is common for a SWG to be unable to keep up with the start of an algae bloom when FC starts at zero. But so long as the water is clear, there can't be all that much algae so it doesn't usually take shock level to get things in line.

Algae growth is exponential, doubling ever few hours, so the rate at which it grows very much depends on how much algae you already have, which is difficult to know. Growth rates also depend on water temperature, higher temperatures cause faster growth, and chlorine levels, higher FC levels cause slower growth.
 
We typically use granular shock, which comes in two sizes, 2lb and 4lb. Since I was only trying to raise the chlorine to prevent algae at this point, I used a 2lb shock. I would guess the pool was around 25000 gallons. I didn't test the chlorine levels after shocking, but my boss said it was very high. If I were to guess, probably somewhere near 20ppm.

As for Jason's comment, I think that's kind of where my head was. Since we are limited to the product line we sell, I went with the smallest does of granular shock I had. I suppose I could have only put in half, but in either case, my boss felt that shock wasn't necessary. I feel somewhat reassured that I was doing the right thing with good reason. Its not uncommon for my boss to pick apart my work, often being inconsistent. He spends too much time trying to save a few cents, and ends up costing himself hundreds of dollars down the road. If I were to go forward with his idea that the shock wasn't necessary, I can only imagine how many green pools we would run into because of it.
 
2 lbs = 32 oz right?

I plugged in 2lbs of trichlor, dichlor, and 73% cal hypo in poolcalculator.com and the highest jump was from trichlor (8.8) based on a 25k gallon pool. What was the cya and did you use tri/di/or cal hypo?
 
The shock we use is trichlor. The CYA level was probably around 50, but might have been as low as 30. I could be slightly off on the volume of water. It was a kidney pool, probably about 18x36. So maybe about 20000gallons instead? But its still not sounding like this shock treatment was an extreme move.
 
Are you sure you are using Trichlor as the shock? Most granular Trichlor takes hours to dissolve so is used mostly as a spot algaecide. There are some products such as Kem-Tek [Super] Shock Quick that are more of a powder and have sodium carbonate in them that helps to dissolve the Trichlor but bubbles a lot and has the chlorine outgas a lot (it smells a lot). It's usually more common to see either Dichlor or Cal-Hypo used for shocking.
 
I like it. It has worked well for me over the years, but I guess if I don't know anything better I wouldn't expect it to work better. We typically pour it into the skimmer so it dissolves on its way through. Never had any problems with it not dissolving that way. If you put it directly into the pool, it will settle and bleach the liner. I'd be interested to hear what you think if you decide to try it out.
 

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In the very first post, you said
The water chemistry was pretty good. pH, TA, CH, CYA, and salt levels were all properly adjusted. I was there to do the first vacuuming so the pool looked perfect for the customer when they got home. I found that the chemistry was all in good shape with the exception of the chlorine levels. Both FC and TC were reading 0.
Click to expand...

How do you know that the pH, TA, CH, and CYA were properly adjusted. How was that done? Are there records of what was done? Is it possible that was not done at all or was improperly done?

(This is why I am so fond of a pool having a record book with all pool specs, all treatments added. Anyone tending a pool ought to have this at hand.)
 
When we fill a new pool, a water sample is taken to the shop. They test for everything and send someone out with whatever chemicals are needed. I also tested the pool when I was there. I don't get to see the records, but there are records kept whenever a sample is run through the shop, and minimal records are kept for weekly services. I do wish I had access to records sometimes. It would certainly make life easier when you show up to a problem pool without knowing the history.
 
I assume that 72% available chlorine trichlor would raise FC less than std trichlor. With a 20k volume and regular trichlor the most FC would rise is 11; 73% cal hypo would raise FC by 8.7... So no you did not overdo it.
 
Its good to hear that I was on the right track. I went to another brand new pool 2 days after he told me I shouldn't have shocked this one. He made a point to tell me not to shock it. Part of me hopes it does turn green. I added clarifier to that pool, and he told me I shouldn't have done that. The pool was cloudy because the pool had just been backfilled and a fair amount of dirt had gotten in. I figured since he wants the customers first time seeing the new pool completed to be a good one, the water should be as clear as possible. He told me that I shouldn't have used the clarifier and that it just needed time to filter. So again, small decision that made perfect sense, and he questioned it. Its really frustrating when my boss criticizes the smallest decisions and micromanages what I do. I've proven myself for 8 years with his company, yet he still feels the need to try to intervene with situations like this. He would do so much better to just get out of my way and let me do my job. He thinks that because he's been in business for 30 years he has all the answers, but from what I've seen he is fairly clueless. I think all he sees is dollars and cents, and when he saw that I used a container of shock, or clarifier, he saw money spent on products that he wasn't billing the customer for. This would come off the profit for building the pool. So instead of him putting $10,000 in his pocket he put $9,975. But by making an issue out of it he knocked down my moral, which in turn kills productivity and will certainly cost him more than the chemicals did in the long run. I apologize for going off on a bit of a rant here. I guess I'm just happy to confirm that I am at least doing right by the customers.
 
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