Why don't I have more problems with algae?

[Titanium]

I have a 24,000 gallon in-ground pool/spa in Northern California.

My latest test results are:

FC normally run between 1 and 5 ppm (I add 1 gal 10% liquid chlorine when I get down to 1-2 ppm. A gallon of 10% chlorine will add between 4 and 4.5 ppm of FC.)
CC 0
Alk 100
CH 400
CYA 160 (diluted my water sample by 50% with tap water and ended up with 80 on the CYA test)
Temp 81
Pump Time 3.5 hours per day (12 noon to 3:30 PM)

Why don't I have more problems with algae? My water is always clear and I can always clearly see the main drain 7 feet down in the deep end. I do end up with a slight green on the walls, but it easily brushes off (in fact the brush causes the green to literally fly away from the walls), and I try to do this once per week, although I have been known to go 2 weeks or longer between brushing. I do end up with white dust accumulating on the steps and bottom of the pool, and I assume this is bleached out algae.

Why am I not seeing green or cloudy water?

I realize that I am running FC at levels far lower than I should given the very high CYA level that I have. And I have considered going higher on my FC, but I haven't since my water looks so good. I have been on BBB for roughly a year, but have only used bleach and muriatic acid so far.

Titanium

P.S. I end up using 2 gallons or so of 10% chlorine per week in the summer and as little as a gallon or two of chlorine per month in the winter.

 

[poolio]

mainly because you stay on top of your water. you can actually maintain fairly low chlorine levels as long as you keep them consistent

 

[JasonLion]

A FC level of 1 to 5 is not enough to prevent algae when CYA is 160. But there are other factors that can limit algae growth. It could be a naturally low phosphate/nitrate level in your pool. From the sound of things you do get algae, it just never grows all that much. A low phosphate level would do that. Plus, as you brushed up and filter out the dead algae you would be constantly removing phosphates, maintaining your low level.

 

[Titanium]

poolio and JasonLion,


Thanks again for your replies and comments. I really appreciate the help.

I reviewed what my Intermatic timer is set for, and I realized my pool pump is actually closer to running only 2.5 hours per day instead of the 3.5 hours I mentioned earlier. I inherited this 1983 vintage pool last year in January, and I actually ran the pool pump more like 6-10 hours per day last summer. I lowered the pool pump time over the winter to the 2.5 hour mark, mainly in order to have some skimmer time and some pressure-side cleaner (Polaris 360) time. And I never increased the time this summer, mainly just to see what would happen, fully intending to run the hours way up again if I started having any water issures. I didn't, so I left things as they were.

The comments about the low nitrates and/or phosphates was interesting, and wasn't something I was even aware of.

So it appears that I am "getting away" with running the pool pump/filter at a fairly minimal level AND running with fairly minimal free chlorine levels. Am I fortunate or what? :-D

Should I leave things as they are? Or would you guys recommend any changes?

Thanks again.

Titanium

 

[poolio]

I wonder what would happen if you didn't run your pump at all? haha jk I was just thinking maybe you have one of those algae eaters in there that you have in aquariums or something. Honestly you really are flirting with disaster and even though the water is clean I would think you are leaving yourself open to bacteria infestation in the water only running it 2 hours a day and not keeping a bit higher chlorine reading in the pool.

 

[gonefishin]

(over the years) What chemicals do you usually use in your pool? Have you ever added anything else to your pool?


I'd agree with the other poster. It sounds like you do get algae...but not a large bloom.


Some things I wonder about is your chlorine strength that you're calling 10%. I know where I get my higher concentration chlorine from is usually higher than the 12% that they call it. They go through alot of chlorine and also test it daily. I know that it can lose its strength quickly...but if your adding 1 gallon at a time...you can go through it quickly as well (you often do you add that gallon of chlorine?)

Also what is the size of the pool. You mentioned the gallons...but what are the dimensions of the pool?



You didn't post your Ph, which seems odd since you've included all other other information needed(even temp)...yet forgot Ph. What is your Ph and does it normally fluctuate (or has it ever in the past?)





With a CYA that high...I'm guessing that you've been using the pucks for a long time. Do you (or have you ever) had a battle with a lowering Ph level? If so...what did you add (do you remember the active chemical?) Was it Borax?

I wonder what your borate level is


thanks,
dan

 

[Ohm_Boy]

Algae isn't the only thing with which you need to concern yourself.
Sanitization is the primary reason for treating the water, and if all your chlorine is locked up in cyanurics or killing algae, what is left to keep your swimmers safe?
In my paltry little opinion, if it were me, I'd bump up my chlorine, and see about lowering the CYA.

 

[JohnT]

Do you cover the pool? Algae needs sunlight, and pool covers can block it out.

 

[Titanium]

John T,

I don't have a cover. There are trees around the pool that start putting the pool in partial shade by 3 PM or so, and complete shade by 5 PM.

----------------------
Ohm_Boy,

I guess that I've been assuming that since I didn't have much of a problem with algae, that the easier-to-kill bacteria were being taken care of in the normal course of business.

---------------------
gonefishin,

I bought this house with the existing 1983-vintage pool in January of 2006. I used the previous owner's supply of tabs until they ran out, and then I started using some form of powdered chlorine. This went on until June/July 2006 which is when I first discovered Pool Forum and realized that the tabs and powder were raising my CYA to undesirable levels. After this point until today, I have only added 10% liquid chlorine and muriatic acid.

The 10% chlorine seems to add betweeen 4 and 4.5 ppm of FC per gallon, which seems in line with the stated 24,000 gallon size of the pool. I typically add a gallon of chlorine every 2-4 days in the summer. I might only add a gallon or two of chlorine for an entire month in the winter when the water temperature gets down in to the high 30's to low 50's.

The pool is irregular in shape, but is roughly 20 feet wide by34 feet long.

My pH was 7.2 last year when I first started using the 10% liquid chlorine. I let the pH drift up to around 7.8 by June 2007. Since then, I have been adding muriatic acid in 1/2 gallon doses and have the pH back down to around 7.3 I typically use the DPD method of testing for chlorine since I find it faster to do than the color comparison using OTO. Since I don't normally break out the smaller "poolside" testing kit, I don't test for pH very often. I have been testing more lately since the pH reduction campaign I have been waging. The pH doesn't seem to fluctuate hardly at all in that I don't see any wild swings. It appears that my water is buffered well such that the pH seems to behave in a well-mannered way.

I have never used borax and have no idea of my borate level.

The previous owner was spectacularly unhelpful in explaining the operation of the pool, or his normal maintenance and/or chemical regime. Everything I've done since June/July has been based on BBB methodology and the visual feedback of the pool water itself.

---------------------

To combat the high CYA level, I contemplated last summer doing a partial drain and refill. However, I thought I would be replastering/retiling the pool before this pool season, so I held off on the drain/refill. I now think that I am going to be replastering/retiling before NEXT pool season, but I may go ahead and do the drain/refill to reduce CYA anyway since my pool remodeling plans seem to keep getting pushed out into the future.

Thanks for all of the comments and observations by everyone.

Titanium

 

[Titanium]

I just reviewed the old pool plans by the builder. The pool excavation was 23'-6" by 36' with a perimeter of 113' and a surface area of 625 sq ft.

The spec's also show a 2 HP pump (probably oversized, but I do have solar panels on a second story roof) with a design turnover of only 3.2 hours. So my pump runtime of 2.5 - 3 hours may not be so out of line as it first appears.

Also, my filter psi shows fairly high at 25 psi without the solar system on, and anywhere between 31 and 35 psi with the solar system on depending on the state of the filter.

Titanium

 

[Guest]

Bottom line is this...you ARE gettin algae on a regular basis since you say you have to brush it off weekly. If you either lower your CYA or increase the FC this will not happen. A properly maintained pool with the right FC for the CYA would not have algae growing on the walls, no matter how little!

 

[Titanium]

waterbear,

Thanks for joining in!

Based on all of the comments I have received, I plan to do a partial drain/refill very soon in order to reduce my CYA levels.

So everybody doesn't get a slight lime-green tint on their pool walls every week or so? I thought everyone did and this was why weekly wall brushing was recommended as part of a normal maintenance schedule. :?:

Thanks again.

Titanium

 

[Guest]

Based on all of the comments I have received, I plan to do a partial drain/refill very soon in order to reduce my CYA levels.

So everybody doesn't get a slight lime-green tint on their pool walls every week or so? I thought everyone did and this was why weekly wall brushing was recommended as part of a normal maintenance schedule. :?:

Thanks again.

Titanium

NO, recurrent algae gowth should NOT happen in a properly maintained pool. It is often a symptom of too high a CYA level.
Brushing is recommened becuase every pool is always fighting nascent algae growth. The chlorine kills the algae if the levels are right but plaster pools have a surface that algae 'sticks' to compared to fiberglass and vinyl and free floating algae is easier for the chlorine to kill than algae attached to the walls. Also, in a plaster pool freqent brushing helps to remove scale before it can build up and cause problems so brushing really serves several purposes. It also mixes the water in the pool to get rid of 'dead spots' of low chlorine and dislodges dirt so it can be either vacuumed out or removed by the filter.