Algae on water feature / rock waterfall - looking for treatment and future prevention suggestions

doberdragon

Member
Aug 27, 2019
8
Katy, TX
So here are my chemistry stats as of today (Katy, TX for climate reference)

Pool built ~ 2008 I believe (we are 2nd home owner for about 1.5 years)
K2006 test kit
FC: 5.6
CC: 0
pH: 7.7 (my water feature is not on a separate pump, so I have it running generally when all the jets are going so my pH rises pretty regularly... I add around 4 cups of MA every few days once it is around 7.8/8.0 and drop it down to 7.2 ish)
TA: 80 (a battle with the pH to keep this above 80, adding acid drops it, so I have to bump this up somewhat regularly as well)
CH: 370
CYA: 50 (I thought this was higher, will work to bring it up closer to 70)
Salt: 3600

I am running the main pump around 8 hours a day - the water feature is on during that time.
I run the polaris 280 around 1.5-2 hours each day.

Any other information you would want to know?

Pool looks like this:


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Pool2.JPG

The issue is I keep getting algae in this rock feature. Algae forms along the water line under the rocks, in a lot of the nooks and crannies, sometimes on top of rocks where water doesn't always flow, and in general spots as you can see. I have spent hours on weekends in the past scrubbing a lot of it that I can with a wire brush and it looks better, but it just seems to come back. I don't really get any other algae issues, I would say sometimes just little specs of green algae on the rocks at the water line around the pool, but this has only happened 2X in the 1.5 years I have owned the pool and it really only seems to happen around the water feature rocks.

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Any suggestions on how to rid myself of this for good?
 
Last edited:

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
10,487
Northern NJ
It's a poor design. You have areas of stagnant water where chlorinated water does not get sufficient flow. It will be a constant battle if you run the water feature daily.
 

doberdragon

Member
Aug 27, 2019
8
Katy, TX
If that is the case, does this algae create any issues for the pool in general then - other than just being a visual nuisance?

Any things you think I could do to lessen it (i.e. run the pump over the water feature less? spray the areas with bleach periodically? any sort of sealants?). I wish I could just powerwash it off and start clean, but with that sandstone style rock, it would just disengrate all over the place and make a major mess, and I assume the areas would be just as prone to future algae again...
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
10,487
Northern NJ
Does your pool pass an Overnight Chlorine Loss Test?

Your water will be very prone to algae if your FC falls below minimum.

If you run the water feature less and let the areas dry out the algae should die out but will probably not fully disappear. I would turn the water feature off for a while, dry the stone areas with a blower, and scrub the areas well with chlorine.

I am a fan of Wet & Forget Concentrate, No Scrub Outdoor Cleaner | Product Information and use it around my pool and house. I would dry the areas out and then treat them with Wet and Forget.

It will take some experimentation to find out what is the least effort way of keeping the algae in check on your water feature.
 

Rich D

Bronze Supporter
Aug 3, 2018
573
MA
I have a waterfall with a small grotto underneath. This is only my second season with it but both seasons I have got one spot of algae in the same spot on one of the rocks in the grotto. I mixed up a batch of 800 PPM chlorine and sprayed the entire grotto area making sure to go heavy on the green stuff. Waited 1 hour and rinsed the entire thing down with pool water no scrubbing necessary. It never came back the rest of the season. All my rocks are granite and probably much less porous than what you have. So if you're going to use a bleach solution I would definitely suggest doing a test rock first.

Now with that being said I do have another theory. There seems to be quite a difference of opinion on phosphates in the pool on this forum. However all agree that they are food for algae. So if you do have high phosphates and the chlorine in the small pools and orifices gets depleted from temp and sun then the algae could thrive there. Especially if you have not totally killed the algae in your prior cleaning attempts. Just a theory.... ¯\_(ツ)_/¯
 

doberdragon

Member
Aug 27, 2019
8
Katy, TX
Does your pool pass an Overnight Chlorine Loss Test?

Your water will be very prone to algae if your FC falls below minimum.

If you run the water feature less and let the areas dry out the algae should die out but will probably not fully disappear. I would turn the water feature off for a while, dry the stone areas with a blower, and scrub the areas well with chlorine.

I am a fan of Wet & Forget Concentrate, No Scrub Outdoor Cleaner | Product Information and use it around my pool and house. I would dry the areas out and then treat them with Wet and Forget.

It will take some experimentation to find out what is the least effort way of keeping the algae in check on your water feature.
Thanks for these suggestions -

I have not done the overnight chlorine test, I will do that and get back to you (going to be out of pocket for ~a week, but can do when I am back. Appreciate that suggestion!

I had not thought about drying out the water feature to try and hit the algae, I had always been keeping it wet when going after it - drying out might make it easier.

With regards to Wet & Forget, do you have any concern if that gets in the pool water? Any idea what it breaks down into over time? I was googling about it and they didn't have a ton of information around this fact that I could find, but I may not be digging deep enough.
 

doberdragon

Member
Aug 27, 2019
8
Katy, TX
I have a waterfall with a small grotto underneath. This is only my second season with it but both seasons I have got one spot of algae in the same spot on one of the rocks in the grotto. I mixed up a batch of 800 PPM chlorine and sprayed the entire grotto area making sure to go heavy on the green stuff. Waited 1 hour and rinsed the entire thing down with pool water no scrubbing necessary. It never came back the rest of the season. All my rocks are granite and probably much less porous than what you have. So if you're going to use a bleach solution I would definitely suggest doing a test rock first.

Now with that being said I do have another theory. There seems to be quite a difference of opinion on phosphates in the pool on this forum. However all agree that they are food for algae. So if you do have high phosphates and the chlorine in the small pools and orifices gets depleted from temp and sun then the algae could thrive there. Especially if you have not totally killed the algae in your prior cleaning attempts. Just a theory.... ¯\_(ツ)_/¯
That is another idea to try on the bleach solution - I have some similar types of rocks that are in the flower bed outside the pool, I could spray and soak on one of those to see if it discolors and go from there.

I know what you mean on the phosphates, I see there is a mixed review on their importance. I do test for phosphates, and put in a phosphate remover low dosage every week or 2. My PPM is generally showing up less than 100 (those tests are tough to read in my book, because the difference in 'blue' vs. 'light blue' vs. 'ultra light blue' vs. clear... is tough for my eyes to differentiate. I figured at least I don't have phosphate to blame as a potential food source, because the level is not registering in my pool.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
10,487
Northern NJ
With regards to Wet & Forget, do you have any concern if that gets in the pool water? Any idea what it breaks down into over time? I was googling about it and they didn't have a ton of information around this fact that I could find, but I may not be digging deep enough.
Wet&Forget is safe to get some into pool water. It will be greatly diluted. Wet&Forget simply changes the pH of the surface to where mold, mildew, and algae can’t live. It is simple and effective.