From clear to algae covered and solid green.... in 3 days!

[1984mountaineer]

Problem: On Thursday evening, I noticed regular crud on the bottom of the pool, so I did my thrice weekly vacuuming. When I finished, the pool was clear as could be with nothing on the bottom or sides, that I could notice. Friday came and went with no one going up to the pool deck. On Saturday, it poured down rain... a couple of inches, in fact. I was heading out of town that evening and got back Sunday evening, late. It also rained some Saturday night, a little bit Sunday and then poured again Sunday night.

When I checked it on Monday morning before heading to work, it was AWFUL. I couldn't really see the bottom and the whole thing was green. I've never seen it like this - or even remotely close. I didn't have time to do anything as I needed to get to work, but threw in a pound of shock (Shock Plus) and decided to take a look at it a couple hours later on an early lunch.

When I got back, it still looked bad, but I could actually see the bottom. It was COVERED in a green film that looked like algae. I took the vacuum out and sucked it up. The bottom was now clear, but the water was still cloudy. I then backwashed and tossed in another pound of shock afterward.

I came back to check it an hour or so later, thinking that with a clear bottom and another pound of shock for the slightly clearing water, it would look half decent. Instead, it was back to solid green - unable to see the bottom or even the skimmer just a couple feet under the water.

I got some algaecide (1 quart) and poured a little bit in the skimmer and the rest around the pool when I got home that evening. I went out this morning in hopes of finding improvement but have not.

I have some reagent to check the PH and CL levels, and all I could tell from that was that my CL was incredibly high and the PH was incredibly low. Up until last week, both were almost always in the "Ideal" range.

I called the pool store and they told me to bring in a sample for a test, saying my results didn't make sense (High CL should mean no algae). I will likely do that when I leave work in a couple hours, but remembering how incompetent they were last time I had a problem (busted hose on the pump), I thought I would check here first. Any help is appreciated. I will try to fill in some of the info below as best I can, being at work and not having much of a water test.

FC:
TC: extremely high
pH: extremely low
TA:
CH:
CYA:

My pool: 20 foot diameter, 4 feet deep, above ground, vinyl
Pool chemicals: chlorine pool, chlorine tablets, shock plus, half bottle of algaecide
My pump & filter: Hayward pump and filter.... sand

[1984mountaineer]

Alright here are some numbers I got from the pool store and what they told me. First off, they did it with the strip and told me that my pH was so low that the computer would not read it, so I won't have all the numbers. Anyways.....

Chlorine: 5ppm (he said this was good)
pH: 5.5
Alkalinity: 0
Hardness: 100ppm
Stabilizer: 0

He told me chlorine was good and the other numbers sucked. I told him it didn't really make sense because we never had a problem with our water until the past few days as detailed above. He told me what didn't make sense was that I had algae, especially as bad as I described it, with the chlorine level that he registered.

His advice was to give me a bucket of alkalinity plus (which would raise alkalinity and pH), pour about half of it in this evening and scrub the walls and bottom with my brush. Repeat with the second half of the bucket tomorrow morning. Then bring in new sample tomorrow evening, but that this would likely be all I need to do aside from a few more bags of shock and just giving it some time.

Thoughts?

[LA Dolphin]

What is your CYA level
what is your cyanuric acid level reading at? If you have a high chlorine reading and have algae then your conditioner/stabilizer:cyanuric acid level is most likely OVER 50%.

[chem geek]

He listed stabilizer (which is Cyanuric Acid, CYA aka conditioner) as 0. I wouldn't trust the pool store numbers, however. Get a good test kit -- either the Taylor K-2006 or the TF100 (see links in many other posts) and read Defeating Algae (link also in many other posts).

[1984mountaineer]

Thanks for the advice on the test kit. Mine is a pretty basic reagent, so it will certainly be something that I upgrade before next summer.

Just thought I'd give an update on the process recommended by the pool store. I dumped in roughly half the bucket of alkalinity plus last night and brushed everything real good. When I went to check it this morning, it certain looks like progress. The water is still pretty darn cloudy, but the greenness is almost all gone. I brushed again and dumped in the remainder of the alkalinity plus.

This evening when I get home, I will check it again, get a sample and take it out to the pool store for another reading. My hope is that things are going along with the best case scenario that was explained to me - that this would get my pH/alkalinity in line and then I would just be able to shock the crap out of it, brush it and vacuum it and it will be back to normal in a day or so.

Once again, any thoughts are appreciated and I will keep everyone updated.