New pool owner battling overnight algae bloom

[SalsaStarr]

I am a new pool owner, taking care of the pool for 2.5 weeks now. I have been adjusting the chemistry based on information found on this site (thanks!). I am using the Taylor K2006 and TF-100 to check levels.

My initial numbers:
7/22: FC 19, CC 0, TC 19, pH 7.7, T/A 130, CH 500, CYA > 100, water temp 68 F

I realized the CYA was very high after reading some posts on the forum. I was concerned that the Chlorine levels were too high as well. The pool had been maintained with an automatic chlorinator using trichlor tablets. I took out the automatic chlorinator, lowered the pH with muriatic acid, and drained and refilled some water (maybe 15%, not sure how much) to lower the CYA level. I have been brushing the walls several days weekly and vacuuming (manual) at least once weekly. The pump (100 gallons per hour) runs 2 hours daily.

Numbers after above interventions:
8/2: FC 7.4, CC 0, TC 7.4, pH 7.6, T/A 130, CYA 90-95, water temp 78F

A few days later:
8/5: FC 6.8, CC 0, pH 7.7

I added liquid chlorine to raise levels by 2 ppm and acid to lower pH. The next day the water was very cloudy and there was a greenish/ brownish tint to the pool. I assumed this was an algae bloom, so I added chlorine to shock level (39ppm for CYA 90) and adjusted the pH.

My question is, am I on the right track, and how long does it take to get rid of algae? The bottom of the pool seemed to have a film of sediment that I vacuumed away today but the water is still cloudy, yellowish, and dull.

Most recent levels:
FC 35, CC less than 0.2, pH 7.5

Also, my kids want to know how soon they can swim again.

 

[SalsaStarr]

My sig didn't show up with the post, but here is the info about my pool: 11K gal IG gunite with Mytilus catridge filter MY-100.

 

[jblizzle]

Welcome

Wow .. so you have both the recommended kits

Seems like you have a pretty good handle on what to do.

Do not adjust pH when your FC > 10ppm ... the test is not accurate.

It can take days - weeks to clear a pool of an algae bloom.

You would be best served by another 50% water replacement to get the CYA down to a more manageable level.

Are you sure the pump is 100 gallons / hour ... that is REALLY slow. I am more likely to believe it is rated to 100 gallons / minute, but likely not actually doing anything close to that. 2 hours is a VERY short run time ... I would guess most people are closer to 6-8 hours per day. And while in the shock process you should be running 24/7.

 

[linen]

Welcome to tfp, SalsaStarr

I'm with jbliz, the first thing I would do is get that cya down lower.

 

[SalsaStarr]

Thanks for the response. I know we need to lower CYA, but we plan to re-plaster in about a month, so we are trying to hold out until then. . . That said, is it okay to drain and refill the pool at the same time one is shocking it?

Any recommendations on what the FC level should be with CYA around 90?

By the way, just when I was wondering if the algae would ever go away, our my pool water is blue again! (still cloudy, though)

 

[jblizzle]

Chlorine CYA Chart tells you the minimum and shock levels. Read the rest of Pool School if you have not already.

Shock level is a FC of 35ppm. And you should never drop below a FC of 7ppm once you finish the shock process.

If you are going to drain in a month anyways, just maintain the levels above.

 

[SalsaStarr]

Thanks everyone. Will do as suggested.

I plan to do the OCLT tonight. If CC remains low (it has been almost undetectable so far) and FC loss is less than 1ppm I am assuming I no longer need to shock. At this point, do I just wait for FC levels to drop and assume it is safe to swim if levels are below shock level (35 in my case)?

 

[jblizzle]

You generally want to stay at shock level until the pool is clear as well to make sure nothing rises from the dead