Crud on walls

[LindaGL]

I've spent the last two weeks pouring bleach into the pool after opening it for the spring. I've done the same thing each year for the last five or six years, and the water has always cleared within a week at most.

I've been holding the FC levels at 14-15 as best I can, checking the water every 1.5-2 hours during daylight. CC ranges from .5 to 1, and there is a loss of FC overnight. (So still killing algae.) CYA levels are below 20 (not registering) but I've been had about 6 pounds of trichlor pucks dissolved when I first opened it a couple of weeks ago, so I know the level isn't at zero.

We opened the filter and reset the sand (which was packed up all around the edges - a result, I think, of the 1.5 hp pump we used to run! I back wash the filter whenever the pressure rises 3-5 pounds, which is about once a day.

This year, the water is not clearing. When I went to brush the sides of the pool, I found them covered with a rough surface (not smooth, as expected with vinyl.) I scraped a spot with a fingernail, and got some off with difficulty. (This stuff is NOT going to come off with just brushing the walls with a nylon brush.) In looking at what I got, it is mostly brown with a bit of green, so I am thinking it is a hard growth of algae of some sort that is not completely dead (hence the water not clearing.)

So the question is - WHAT is this stuff, and how do I get it off the sides of an AG pool?

 

[waste]

Welcome to TFP!!

If you could post some test #s, we can tell if it's calcium build up (which I think it may well be). Without test #s, we're just guessing, but with them, the experts here will not only diagnose the problem but tell you how to properly fix it 8)

 

[LindaGL]

I knew <G> you were going to want a complete test. Here are the most recent numbers, from a water sample I just pulled:

FC: 12.5 (that's down about 1.5 ppm since the sun set four hours ago)
CC: 1.0
TA: 170
CH: 130 (tested this twice to make sure of the number)
pH: 7.2 (this number is down from 7.4 or so two days ago)
CYA: <20 (not registering on test)

I find the drop in pH interesting - I have added three boxes of borax in the last two weeks, and am having trouble getting the pH to come up. Normally it runs high, and I have to add acid to lower it. This is the first time I have ever had to RAISE it. I have added several inches of water due to all the backflushing, which I guess might be lowering the pH faster than the bleach is raising it.

I didn't think the CH level was terribly high - and looking back over my past several years worth of test results, it has always run in the 130-140 range. Out of curiosity, I ran the same tests on my fill water (well water) and got the following:

FC: 0
CC: 0
TA: 260
CH: 210
pH: 7.2
CYA: <20 (no results)

So - how can the CH be higher in the fill water than in the pool results?

And now, any suggestions on what is attaching itself to my walls?

 

[duraleigh]

Linda,

What condition was the pool when you closed last fall? Clear Water?

It appears you have algae growth and very possibly a mineral deposit. Well water is a frequent culprit for iron deposits in swimming pools......have you tested for iron?

 

[frustratedpoolmom]

The CH can be lower in your pool from rain dilution...even with adding fill water from your tap.

In the past your PH rises because you have very high TA. You can read about lowering TA in Pool School, you may want to consider this for the future if you notice it happening again, not sure what is causing the opposite right now.

If your PH has been high in the past that may have somehow contributed to whatever is happening to your walls, not sure.

 

[JasonLion]

That sounds like calcium scale with algae growing in the rough calcium scaled areas. Calcium scale will feed like stone or grit, while anything created by algae alone will be slimy or at least softer. You can confirm that it is calcium if you can scrape a little of it off and then put a drop of muriatic acid on that. If it contains significant amounts of calcium the muriatic acid will foam up.

Your TA level is very high, which could have been enough to cause a problem even though your CH level is reasonable.

I suggest you start getting your CYA level up to at least 20 or 30 right away. With CYA very low you will be losing a lot of chlorine to sunlight everyday. Raising the CYA level to 20-30 will cut down on the amount of chlorine lost to sunlight dramatically.

If your currently very very high FC levels (because CYA is low) has not killed the algae yet, it may take removing the scale to completely kill all the algae. Towards that end, you will need to start on lowering your TA level. See this article at Pool School. Just keep in mind that the PH will read a little higher than actual when the FC level is 10 or higher, and the PH test tends not to work at all when FC is above 20, so lowering TA while maintaining shock level can be a little tricky.

 

[LindaGL]

Thanks guys -

The water was clear when I closed. The growth on the walls is new over the winter - and it is definitely gritty, not slimy.

I don't have any acid on hand to test, but I agree it sounds like mineral deposit. As for the cause, I'll take your word for it, but I do have to wonder. The pool has been open for 7 years without a similar problem and my TA level has always tended to stay in the range of 170-180. The ONLY thing I have done differently this year is add the Borax, and I did that when the pH dropped below 7.0. What I don't know is whether the walls were rough before I added it, because I didn't think to feel them below the water level until yesterday. I presume they probably were.

Anyhow - from what I am reading, the plan first should be to get the CYA levels up (I have CYA - I was waiting to add it until I got the algae cleared up.)

As the CYA is dissolving, work to get the TA reduced without overly worrying about the algae. (Since the last two weeks seem to be telling me I won't kill the algae until I get rid of the deposits.)

Then once the TA is reduced, worry about the algae.

Lowering the pH lowers the TA, aerating raises the pH without raising the TA. Right? How low can I let the pH go without worrying about the vinyl liner?

If I get the TA reduced, will the deposits resolve on their own? If so, any idea how long it might take? (I can't begin to imagine scraping them off by hand ...)

 

[duraleigh]

Hi, Linda,

It does sound like calcium, but, like Jason said, your numbers are not really conducive to calcium deposits.

I assume you have filled from the well for the years you have had the pool so I'm reluctant to point at the well as the culprit.....altho it certainly could be.

I don't think you will have much luck removing the depositis until you get them identified. HD/Lowe's has muriatic and I would suggest you try that (or a pool store) Removal method of the deposit will differ depending on what it is.

Getting your TA in line is not likely to have any effect on the deposits.

 

[JasonLion]

It takes quite a while for calcium scale to form, it isn't something that could have happened in the last few days.

It sounds like you have a good grasp of the TA lowering process. With a vinyl liner, I wouldn't take the PH down below 7.0.