Hello all,

I was maintaining the pool at FC 6 (PC says FC 4-9) and started getting spotty algae breakouts. Shocked and raised the FC to 8 and the algae dissapeared for a while. The it appeared again in the the same spot and its vicinity which is near the spa spillway next to the steps of the pool (shallowest part of the pool). Shocked, and raised the FC to 10 and algae dissapeared again only to reappear as soon as i brought down the FC to 8. This time it appeared in other parts of the pool also.

Here are the parameters of the pool when i got the last algae:

FC 8
CC 0.25 (barely pink solution)
TA 70
pH 7.6
CYA 55
Bor 40
CH 390

Last night I raised the TA a bit and have started shocking the pool again. the temperatures in this whole scenario has been rising and the last outbreak of algae was a few days into the heat wave with pool temp 87 F.

Also the CH has risen from 290 in June to 390 yesterday. Pool has been needing water but just like last year though.

Above all, this season we have used the pool only once! So there has been no bather load around the times of these algae outbreaks. There has been no change in circulation rate or pattern.

Current parameters:

FC 24
CC 0.25
TA 80
Bor 40
CYA 55
CH 390
Temp 88F

I must admit that I had been letting FC drop to 4-5 before these outbreaks but that is still within range according to the pool calculator.

Any ideas?

Thanks!

Based on the first half of your post, you should review the shock process as outlined in Pool School. Maintain the shock level FC for your CYA until you pass the three tests to stop. If you then maintain the FC above the minimum, no more algae should appear.

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Thanks for the reply!

I am doing that right now as we speak. When this started, what was weird was that cc used to be 0 in tests and i could see green algae in spots.

Sometimes it doesn't seem like CC goes along with exactly what is going on in the pool... that is why there is more than one criteria for determining a healthy pool. They say too that algae can put a film over itself to protect itself from chlorine so long as it is not disturbed. Could be the reason for your 0 CC.

How are you getting a CC result of 0.25?

While doing the FC test I determine how much one drop of r871 causes the pink to disappear when the solution is just turning clear. Then I keep an eye on how pink the solution gets with r3. If the pink was really faint with r3, and disappears with one drop of r871, I call it 0.25.

It is totally inference and you can still note it down as 0.5 rather than 0.25 if you'd like.

Gotcha... I've had those results too. I don't bother to spec them at 0.25 but I see the logic.

What are the other criteria for a healthy pool? All I know is CC and keep CSI in range while keeping other parameters in range from pool calculator.

What else should I watch out for?

Thanks!

Suley:

Another test you can run periodically is the Overnight Chlorine Loss Test (see OCLT link in my sig). Chlorine is consumed by two things: sunlight and organic matter. By running this test at night, sunlight is eliminated as a contributor to chlorine loss. Even if your water is clear (a good sign), that alone cannot conclusively rule out the presence of small amounts of microbial activity (http://www.taylortechnologies.com/FeatureArticleCM.ASP?ContentID=93 See Myth 1). Hence the need for various tests such as OCLT, along with FC/CC levels.

Continue keeping your pool water in balance my monitoring pH, TA, and the other parameters of the CSI even during the off-season if you keep your pool operational year-round (which is probably likely in LA).

Thanks Bo! I found that myths article to be very informative.

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