Algae with perfectly balanced water?


Active member
Jun 10, 2008

About 2 weeks ago, I drained my pool and installed a Pentair IC-60 SWG. I have been testing (with my TF-100) daily and everything looks perfect. When I first drained the pool, I had some residual mustard looking algae (not a lot, but is was slightly noticeable on hoses and what not). So I cranked the brand new SWG to 100% and let it run 24/7 for like 3 days. At that time, CYA was at maybe 10-20 and my FC was at 21. Figured that would kill anything.

For the last 10 days or so, FC has been rock solid at 3.5 - 4 ppm. I run the SWG while the sun is shining, as I figure that is more stable with the FC.

Today, I went for a swim and found some REALLY dark colored algae on the steps. Almost like black slimy spots that are smaller than a dime. What am I doing wrong?
Should I maintain a higher FC level? I can't seem to even scrub this algae off of the pebbletec. I wouldn't say there is a lot of it....just a couple pretty small areas (mostly by steps) - just surprised it is there at all.

Pump runs the SWG (set at 60% output) from 7AM - 3PM (after it runs on high for 2 hours for the Polaris)

FC = 3.5 - 4 ppm (test is every night before bed and it is ALWAYS in this range)
Ph = 7.5 (swings widely - I drop it to 7.2 at it is back at 7.7 within 2 days)
CYA = 50
TA = 80
CH = 260
Water Temp = 91 F (it's hot here in AZ!)

I was soooo excited to install the SWG and make life a little easier. Now I can't figure out what happened!

I also just installed a new filter and am running Zeosand. I had the filter bypassed for 4 days, but was still running the pump and SWG. Don't think that is part of this, but throwing it all out there.

Thanks for your help!!!
Last edited:

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
The algae you're seeing will never truly go away until you completely kill and remove it following the SLAM Process. That's going to be key. Cranking-up the SWG simpy won't do it. You'll want to give the SWG a break and rely on regular bleach to perform the SLAM. With a CYA or 50, your SLAM FC level needs ot be maintained at "20" per the FC/CYA Chart until you pass all 3 SLAM criteria.

Once the SLAM is completed, increase the CYA to 70 as is recommended here at TFP for SGW pools. Good luck!
  • Like
Reactions: Msch99


Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
Bedford, TX

You are in AZ, your CYA should be 70 or above, as low CYA will cause your FC to burn off very quickly.. I am amazed that with a CYA of 50, you are not using more FC than it appears you are...

I see the saltwater CYA/FC chart a little different.. FC/CYA Chart I see the minimum as some place I do not want to get near... I always try to keep my FC at or above the target. If I shut my pump off, I'd want my FC to be high enough that when the pump came back on, my FC would still be at the target level.. not down at the minimum..

As far as pH goes, you are just spinning your wheels.. SWCG pools like their pH to be 7.8 or so.. Just let it sit at 7.8 until it drifts up to 8.0 and then only knock it back to 7.7.. It will work much better for you.

I agree with Pat.. Do a SLAM with your lower CYA and then bring it up.


Jim R.


Active member
Jun 10, 2008
Thanks to both of you for replying.

I will do the SLAM process and then increase CYA and keep the FC a little higher.

Jim - For some reason, I thought having FC too high was bad for the metal in the pool, so I was trying to hold tight on the target and my "minimum" was always slightly above the listed minimum. I see that life can be a lot easier by bumping up the FC 1-2 more. Then I don't have to test every night and worry about it so much.

Thanks again!