Help with my Algae problem

[tonecold]

I have an above ground pool that is about 9800 gallons. I'm using a 6-way HTH test kit to test my water.

I keep getting green algae on the bottom of the pool despite keeping my chlorine level up. I know I'm missing something here so hoping that someone can point me in the right direction. According to the HTH kit my numbers are...

Cl -5ppm
PH - 7.2
Alk - 100ppm
CYA - 40ppm

I have a 250lb sand filter and a 1hp pump that I run pretty much 24/7. I started out the season with something that looked like the black lagoon and using bleach was able to get the water clear. Every other day I've got green algae on the bottom of the pool though. I've tried shocking with the granular shock and also keeping pucks in the water but still no change. I vacuum the algae to waste but in doing so, stir some of the algae on the bottom which turns my water blue/cloudy.

[aylad]

If you have recurrent algae despite a chlorine of 5, then you have a bloom somewhere that has not been completely killed off. Shock your pool up to about 15 ppm, and hold it there until there is no more green algae by testing 2-3 times during the day and adding more bleach to get back up to that 15 ppm. Brush it daily, as well. Once the algae is all dead, you can filter it out, and as long as you maintain your Cl at least 3-4, you shouldn't have problem with it coming back.

Janet

[chem geek]

tonecold,

Since your case is the only one I have ever seen where keeping sufficiently high chlorine levels would not keep away green algae, I've been thinking more about it and I believe I may know what is happening in your situation. I suspect that in your above-ground pool that you do not have a floor drain, but only have a skimmer (and a return, of course). So perhaps the circulation is very poor in the depths so that chlorine concentrations are low there, especially when the algae wasn't completely killed (as Janet pointed out as a possibility). Though keeping a higher concentration overall will increase even the concentration at depths, an easier solution would be to improve circulation through pointing the return down and to the side to try and get a spiraling effect. Also, using a pool sweep regularly to mix up the water might help. Manual solutions include regular brushing to mix up the water -- or just using the pool every day including deep diving!

Anyway, I could be wrong about this, but wanted to offer some suggestions. You might try inverting a container and with a grabber tool take it to the depths not far from the algae, then invert the container and bring it up to measure the chlorine level down there. That would help confirm or dispute my assertion. Janet's recommendation for shocking is still appropriate since getting rid of the chlorine demand from nascent algae should help.

Richard

[tonecold]

I'm now on day 3 and I've kept my chlorine levels very high. My HTH test kit will only test up to 5ppm. I don't have any distilled water to accurately test the shot glass method (I'll be picking some up later today) so I used some bottled drinking water instead. It shows that the Chlorine level is above 15ppm.

I've added about 12-14 gallons of bleach during this time. While there may have been a couple hours where the levels dropped while I was at work, I'm guessing that it never dropped below 10ppm.

The water has cleared up pretty well with the bleach and the pump running 24/7 (still cloudy) but sure enough, I came out this morning to notice a greenish film on the bottom. Not as bad as the previous days but it was still there. I've brushed several times a day for the past couple of days and even left the vacuum in the water overnight so it would continue sucking water from the bottom of the pool rather than the surface by the skimmer.

Here are my numbers now:

CL 16-20ppm
CYA 40ppm
Alk 120
PH 7.5

I'm going to try some polyquat and see how that works. Of course, its now the hottest day of summer and the pool is out of commission

[tonecold]

Here is a picture of what I've got after day 3. I just vacuumed but left a spot on the middle so you can see the green tint.

[chem geek]

Is your HTH test kit using test strips or liquid drops for testing? Specifically, for the CYA test do you mix half pool water with half CYA reagent and then mix for 30 seconds and then pour into a tube until the black dot at the bottom is no longer visible? Or do you measure some color on a test strip? If the latter, CYA test strips tests are notoriously inaccurate. I suggest you get yourself a good test kit, the Taylor K-2006 from Taylor here or from Leslie's here or other stores or you can get a kit similar to what Ben used to sell on this site at tftestkits here.

Also, from the picture it looks like there is no floor drain so while shocking have you been using a pool brush to mix the water in the pool, especially in the region near where the greenish color is showing up at the bottom? Have you tried running your pool sweep during this time?

Richard

[tonecold]

Is your HTH test kit using test strips or liquid drops for testing? Specifically, for the CYA test do you mix half pool water with half CYA reagent and then mix for 30 seconds and then pour into a tube until the black dot at the bottom is no longer visible? Or do you measure some color on a test strip? If the latter, CYA test strips tests are notoriously inaccurate. I suggest you get yourself a good test kit, the Taylor K-2006 from Taylor here or from Leslie's here or other stores or you can get a kit similar to what Ben used to sell on this site at tftestkits here.

Also, from the picture it looks like there is no floor drain so while shocking have you been using a pool brush to mix the water in the pool, especially in the region near where the greenish color is showing up at the bottom? Have you tried running your pool sweep during this time?

Richard

I'm using the drops. Yes, I use the drops half water/ half CYA reagent to test CYA.

There is no drain, just a skimmer and a return. I've been brushing/vacuuming at least 3 times a day.

I'm going to order a better test kit. Just hoping I can get this under control before the new kit arrives.