I have Nitrates...pool store says drain the water

Jun 6, 2008
I am new and I really need some guidance. I have a 4.5ft x 24ft above ground vinyl pool. When I bought my house it had a nice cover on it, but I later found out that it has sat neglected for years and they just covered it up. I wound up draining it, replacing the liner and the pump and sand filter. I fought all summer trying to get my water clear and never quite got there. This year I took my cover off and I was so excited that the water was clear with a small amount of debris on the bottom. It was ok for a couple of days and then once again green and cloudy like last summer. Over the past month i used a 25lb bucket of shock trying to get it clear. My chemical levels are always good but no clear water. The man at the pool store decided to check for nitrates and he said they were high (can't remember the #) and that I need to drain and refill. I turned the pump off for a few days and drained down to below skimmer until I had time to drain and yesterday I noticed that there was clear water with a green coating on the bottom. I put my Pool Rover in to clean it and it stirred it back to look like what it had been before I turned off the pump. Does that sound like a nitrate problem to you or more of an algae problem?

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
San Rafael, CA USA
First of all, welcome to the TFP forum!

I don't know what kind of test kit you have or whether the pool store ran tests and gave you the info, but what we are looking for are the following numbers if you know them:

Free Chlorine (FC)
Combined Chlorine (CC) or Total Chlorine (TC)
Total Alkalinity (TA)
Cyanuric Acid (CYA)
Calcium Hardness (CH)

Your 4.5 foot x 24 foot vinyl pool is approximately 15,000 gallons. Do you know what kind of chlorine you were using from that bucket for shocking the pool? Was it Cal-Hypo or was it Dichlor? If it was Cal-Hypo, then 25 pounds would cumulatively add 128 ppm to FC and 91 ppm to CH. If it was Dichlor, then 25 pounds would cumulatively add 111 ppm to FC and 101 ppm to CYA which wouldn't be good (that much CYA, that is).

While you are gathering your info, you can read the Stickies listed at the top of this forum, especially this one on clearing a green (or cloudy) pool and this one on info to include in a post.

If you do not already have a good test kit, we highly recommend either the Taylor K-2006 kit you can get at a good online price here or the TF100 test kit here with the latter kit having 36% more volume of reagents so comparably priced "per test". The TF100 uses Taylor reagents, but is packaged with a more intelligent combination of reagent quantities and has two types of chlorine tests.



TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
Welcome to TFP!

You might want to do a small scale test to see how much chlorine is required to clear up the pool. Get a 5 gallon bucket and fill it mostly full with pool water. Add one oz of 6% bleach and mix it in for a minute. Wait 30 minutes and then test the FC level. If the FC level is below 10 repeat the process (adding another oz of bleach to the same water sample). If the first oz results in a high FC level try again with a new sample but this time use teaspoons instead of oz. The number of oz/teaspoons of bleach you need to use will show about how much chlorine is required to clear the pool.


Nitrates are algae food so a nitrate problem IS an algae problem. They are also hard to get rid of. It can take very high chlorine levels to destroy them, often too high fir a vinyl liner so if you are not able to get rid of them by shocking you will need to do a series of drains and refills to dilute them enough to get them to where they do respond to shocking