Algae ?

[aylad]

but they have a pc. of paper on the wall that says they graduated from pool water chemistry school.
It looked impressive.

Don't be too impressed--somebody there may have graduated from pool water chemistry school, but they're also in business to make money. Besides, I find it odd that nobody that works at our local chain of pool stores actually owns or has ever taken care of a pool!!

But that's beside the point.........

I still think you have sand or other debris that's just settling out of the water, or that you have sand blowing into the pool. Even though your filter sand is white when it goes in, over the course of time and filtered "junk" it will darken and can appear brown/tan. Might be worth tearing down the filter again to check for lateral problems. Also, do you have a multiport valve that may need a new gasket?

When you run a set of tests tonight, check for free and total or free and combined chlorine. Also, if you'll test tonight after the sun goes down and test again in the morning before the sun hits the pool, that will tell you if there's something organic in the water--you'll lose more than 1 ppm. If you're not losing any chlorine, then you've just got debris in the water.

You'll do yourself a favor if you get that CYA off the bottom of your pool, either by vacuuming to waste or at least get it into the filter. Personally, I'd go to waste.

What hp rating is your pump?

Janet

[chem geek]

Pool water chemistry school doesn't mean that they know all there is to know nor that everything they know is accurate. Even the NSPF CPO course has some errors and a lot of omissions. I write about this in the following post:

http://www.troublefreepool.com/certi...ht-t18432.html

I am also going through the IPSSA Basic and Intermediate Training Water Chemistry manuals and they have similar errors and omissions.

The biggest problem is a complete lack of understanding of the chlorine / CYA relationship which is a primary principle of BBB that keeps all our pools algae-free at low cost.

[CarlD]

Sadly, the pool biz is filled with as much mis-information and false advertising as the vitamin and supplement biz.

Ben started this site because the pool industry and pool chemical industry regularly distributes information that is false and mis-leading. Even the EPA has blatantly incorrect guidelines for chlorine levels. Just some examples:

1) you need calcium in your water even with a vinyl pool: FALSE!
2) If you get "chlorine lock" you need to drain your pool and refill: FALSE!
3) Bleach adds to your total dissolved solids and therefore should NOT be used: FALSE!
4) Phosphates are a serious problem and you need phosphate removers if you want a clear pool: FALSE!
5) The bigger the pump, the better: FALSE!
6) Nature2 will save you money by cutting your chlorine use in half: FALSE! (the cartridges cost double the cost of the chlorine you save)
7) You lower Total Alkalinity by using the "Slug" method of adding a lot of Muriatic Acid in one place: FALSE!

That's a sample of 7 things that are pushed on you by the industry that are false and I can think of half a dozen more, easily.