Algae growing in rock waterfall

[jennacarly]

I have green algae growing in the "pools" of water in my rock waterfall. I do not see any algae in the pool yet. The waterfall runs for 1/2 hr each night. I have an SWG. My latest test results using the kit recommended is:

pH 7.8 ( I just added some acid after this result)
Cl 2
CYA 50-60
TA 50-60
CH 330

The SWG is running at 30%. I plan today on getting some stabilizer and some baking soda to add in to increase my CYA closer to 70 and TA closer to 60. From what I have read in pool school I need to shock the pool with a lot of bleach. However, I will not be able to do this and properly monitor the pool until after Easter. Will it be OK to wait until then to shock or does anyone have any other recommendations?

Thanks in advance!

 

[jennacarly]

I just did the FAS-DPD test and the CC result was 0.5. Is shocking necessary or should I just add some algaecide to the pools in the rock waterfall?

 

[chem geek]

A CC of 0.5 is fine -- if you were to use the 25 ml sample size instead, you'd probably find that the CC is only <= 0.2 ppm or perhaps <= 0.4 ppm which is also fine. No need to shock because of that.

The main problem is that the pools don't get enough circulation to keep chlorine from dissipating and then algae is able to grow when the chlorine level gets too low. You can try just adding chlorine to the pools to shock them (it shouldn't take very much since their volume is small) to at least kill off the existing algae, but longer term you need a different solution. You can either run your waterfall more frequently to refresh it with more chlorine throughout the day or you can run it infrequently and use a safe algaecide such as PolyQuat 60 you add to the pools or possibly use 50 ppm Borates (a very small amount added to the pools). However, the algaecide won't stay in the pools when you run the waterfall (i.e. it will get diluted) so will need to be replenished periodically so probably not the best solution.

If you used 50 ppm Borates in your pool overall, then that would also remain in the small pools in the waterfall and at least help to inhibit algae growth somewhat. However, it still might not completely prevent the growth you are seeing -- depends on how frequently you run the waterfall to replenish the lost chlorine.

The higher CYA level will somewhat reduce the chlorine loss from sunlight and that will help a little, but not that much since you aren't raising it very much.

 

[jennacarly]

Wow chem geek, you're fast! Thanks for the peace of mind. I will add bleach to the pools and add borates to the whole pool as well.

I was hesitant to run the waterfall more often because the builder has it on a separate 5 HP pump and I was afraid it was an energy hog. Do you think running it for 10 minutes three times a day will work instead? I don't know how long it takes for the chlorine to evaporate.

 

[danivdp]

Not a pro, but I'd keep a spray bottle with regular clorox in and just spray the thing down whenever it starts looking a little green or feels slimy. That is what I do for my non-pool related patio waterfall/fountain. Just another maintenance thing that you'll have to do like cleaning the skimmer basket, YK? I wouldn't mess with borates unless I had to.

You could try the 10min 3x a day thing and see if that helped. Doesn't hurt to try!!

 

[chem geek]

I think that 10 minutes 3 times a day might work if the waterfall pools are small and the waterfall isn't just a dribble.

I noticed that your pool is rather large at 54' x 25' so adding borates to the entire pool won't be cheap. On the other hand, you've got an SWG so if you find that the pH tends to keep rising over time in spite of trying to keep a lower TA level, then the borates can help at least reduce the frequency of acid addition.

danivdp's advice is good if you are willing to add this to your maintenance routine since it certainly is less of a more permanent commitment such as the borates. However, spraying would work well for algae on the rocks, but it sounded like you've got algae in the pools themselves under water. For that, just adding some chlorine to the pools would work, but again would need to be every day. Running the water fall for a short time during the day might be enough to avoid having to do this manually.