CYA >100. Can I drain from top and fill from the bottom?

[muski]

First post -- hope I'm providing the right info...

I have a 25,000 gallon IG plaster pool (c.1963) with a cartridge filter. Non-permeable safety cover usually on all but one hour a day. I've been using 3" tabs for the past three years and I think they've finally caught up with me. Here are my current test results (I used a Taylor FAS-DPD, then also took a water sample to the pool store, who got identical results):

FC: 0
TC: 0
pH 6.8
TA - 130
CH - 350
CYA - 110
No copper present

So two big problems -- high CYA and low pH. For a few years my pH was too high, but in the last two years it's been acidic. Only thing that changed was a switch from Costco tabs (made by Dupont?) to Leslie Tabs, and maybe the cover is on more often? I've tried correcting with Soda Ash a few times, but never really got the pH back where I wanted it (and the pool goes cloudy for a few days). But given my CYA level now, I think it's time to do a more major water change. (I've never changed the water completely in the five years since I bought the house).

Problem is I have small children and never leave the cover off when the pool is unattended. I don't like to drain the pool too much with the cover on as it really sags and puts a lot of pressure on the tracks. The pool store guy said that if you turn the pump off for >8 hours, the CYA will rise to the surface, so that you can then drain from the top (with a pump on the top step) while simultaneously filling from the bottom. I was thinking of getting two flow meters to match the in/outflows on the pump/spigot to keep the water level about right.

Bu then I've read one conflicting post somewhere that said CYA was heavier than water and so dropped to the bottom of the pool...

Has anyone ever tried this? Think this might work?

Thanks.

P.S. I'm going back to liquid chlorine once I get this sorted...

 

[Isaac-1]

Re: CYA >100. Can I drain from top and fill from the bottom

Welcome, and sorry for your problems, your problems likely come from using trichlor pucks, they add FC and CYA to the water and are also acidic. As to the rest, there is no truth in the rumor that CYA will float up to the surface if circulation is turned off, I am not sure how this one got started, but I suspect it has something to do with the over simplified concept that CYA is like sunscreen for your pool. As to filling at the bottom and draining from the top when there is no circulation this, can help keep the fresh water separate from the fill water as cold water sinks and warm water rises, however this is only true if your fill water source is at a temperature well below the pool water. If they are both within a couple of degrees of each other then this is not going to help, and if the fill water is warmer than the pool water you would want to do it the other way around draining from the bottom and filling from the top.

Ike

p.s. with your current lack of FC and high CYA there is a good chance something is trying to get started growing in your pool hence the cloudy water

 

[Butterfly]

Re: CYA >100. Can I drain from top and fill from the bottom

Welcome to the forum

Did you do the dilution test for the CYA? The CYA test is pretty accurate up to about 90, but will read anything that is 100 or over 100 as 100.

Also, you don't want to use soda ash to raise pH as it will also raise TA. We use borax to raise the pH, as it has very little effect on TA. 20 mule team borax from the grocery store:

 

[Bama Rambler]

Re: CYA >100. Can I drain from top and fill from the bottom

Welcome to TFP.

Since the other two have most of the problems covered, I'll go ahead and tell you that you need your own good test kit. Given the history of the chlorine you've been using, there's no telling what your CYA is.

 

[duraleigh]

Re: CYA >100. Can I drain from top and fill from the bottom

however this is only true if your fill water source is at a temperature well below the pool water.

Yes, but this time of year it almost always is. Fill water temp coming out of the ground should be about 65-70 or so. Pool water should be quite a bit warmer than that or you live in Alaska. :lol:

 

[muski]

Re: CYA >100. Can I drain from top and fill from the bottom

Our pool is solar heated to 88F right now and the tap water is pretty cold, so I bet I can do a reasonable water change by filling from the bottom and draining from the top. I'll give it a shot.

I'll switch to Borax -- good tip. I'm using a Taylor K-2006 kit. I thought this was an ok kit? I thought if it gave me a CYA reading in the 30-50 range after the water change I'll be ok.

Thanks for everyone's help. I'll report back.

 

[Isaac-1]

Re: CYA >100. Can I drain from top and fill from the bottom

Dave I agree the temperature issue is usually not a problem for most people, however I do know of places here in the south, particularly places with above ground water tanks nearby where the "cold" tap water can get surprisingly hot.

 

[chem geek]

Re: CYA >100. Can I drain from top and fill from the bottom

If you don't want to do a partial drain/refill, then to be more efficient for continuous dilution you can drain from one end of the pool and add water at the other end. If the pump is off, the rate of mixing will be slow so you'll get somewhat more efficient dilution. Just forget about CYA naturally rising or falling or anything like that. With no circulation you are looking at diffusion which is very slow, but thermal convection still occurs but that's mostly vertical -- hence the recommendation to go horizontal with the adding at one end and draining from the other.