Dark line at and above waterline - algae?

[JenniferMarie90]

Hi all. I have a SWG my CYA is 60, free chlorine is 4 and pH is 7.3. Im noticing this weird dark cast at abd right above my waterline. Im having to scrub the heck out of it every weekend despite having a pool robot. Right below the waterline my light tiles are nice and bright. When I scrap the dark like with my fingernail it looks green like algae. My CYA was quite low at 30 for around start up and just recently I was able to bring it up to 60. Pool was finished and started in April. The PB suggested light tile for less maintenance and here I am scrubbing all the time ugh. Any insight?

 

[Rancho Cost-a-Lotta]

That was my plan...having calcium-colored tile so I wouldn't have to worry about calcium scaling at the waterline. The wife wouldn't go for it. Oh well.

I bet what you're seeing is scum from the environment and suntan oils/lotions. It's the same stuff I see in my bright white skimmer. Green or yellow algae would wipe right off. Black algae likely wouldn't grow there.

If you suspect algae (rising filter pressure, cloudy water, excessive FC loss), it would be best to do an Overnight Chlorine Loss Test. You can try to float scum sponges in the skimmer to absorb some of the grime floating around and buy some beer and Motrin to ease the effects of scrubbing.

I really like your tile choice!

 

[JenniferMarie90]

Thank you, I liked it Initially a lot but with its looking so grimy idk anymore. It takes quite a bit of elbow grease to get it off like I tried brushing with a nylon brush and sometimes that works but today I had to use an abrasive sponge. I do see a little green on some of the grout lines too. I run my pump at night which is when the SWG runs would an overnight test still be a valid test? Thanks for the help. In the meantime I’ll get some of those sponges

 

[mknauss]

Any specific reason you run your pump overnight?

 

[Rancho Cost-a-Lotta]

I do see a little green on some of the grout lines too. I run my pump at night which is when the SWG runs would an overnight test still be a valid test?

The SWG will need to be off for the test. About one hour before sunset, add 4 to 5 ppm of liquid chlorine with the pump running. Allow time for the chlorine to mix. Test FC after sunset and again prior to sunrise. Compare the results. A loss of 1 ppm or more indicates something organic in the water consuming chlorine.

Not sure what the green stuff is in the grout lines. Dark green/black could point to black algae, which is actually more of a mold. Try to post some pics and maybe we can help.

 

[JenniferMarie90]

Any specific reason you run your pump overnight?

It’s cheaper, I work for an electric utility and it’s cheaper per kWh over night. I am thinking of running it 4 hours at night and maybe 4 hours during the day to keep a more consistent chlorination

 

[proavia]

What brand, model number and capacity is your SWG?

What happens if you put some bleach or liquid chlorine on a plain sponge and wipe this dark line? Do this on the grout lines too. Rinse tile and sponge with pool water when done.

 

[mknauss]

It’s cheaper, I work for an electric utility and it’s cheaper per kWh over night. I am thinking of running it 4 hours at night and maybe 4 hours during the day to keep a more consistent chlorination

In Las Vegas? I did not know that Nevada Energy had any TOU pricing.

Edit - I see they do. As a customer, I had no idea.

If you are generating all your chlorine at night, you need to target much higher FC to be sure you never go below target during the day when your pool is losing its FC but you are not making any. The potential for FC loss at the pool surface with our extreme UV is very high. Also, you should be able to get your VS pump down to less than 200 watts when running. Compared to your air conditioner, the pump usage is not even noticeable.

 

[JenniferMarie90]

In Las Vegas? I did not know that Nevada Energy had any TOU pricing.

Edit - I see they do. As a customer, I had no idea.

If you are generating all your chlorine at night, you need to target much higher FC to be sure you never go below target during the day when your pool is losing its FC but you are not making any. The potential for FC loss at the pool surface with our extreme UV is very high. Also, you should be able to get your VS pump down to less than 200 watts when running. Compared to your air conditioner, the pump usage is not even noticeable.

That makes sense. I usually test my chlorine around 5 pm every few days and with the pump running until about 6am the FC is right around 4 which I thought was pretty considering like you said the water is in the UV all day. I’ll switch it up and try having the pump on for a few hours during the day too, see if that helps. After swimming in the pool on Saturday and scrubbing the tile, I woke up to a Michel more intense line. I will admit I wear a lot of sunscreen so I dont know if this is just “grime”. It wiped off easily.

 

[mknauss]

That picture looks like oily grime. Suncreen, hair products, etc.

 

[proavia]

Be sure your pump has been running for at least 30 minutes prior to pulling a water sample for testing to insure getting a representative sample. Consistently take the sample from the same location (away from any returns) and about 18" below the surface.

 

[JenniferMarie90]

That picture looks like oily grime. Suncreen, hair products, etc.

Ok that’s good news to me lol better than algae

 

[mknauss]

Try Simple Green to clean it off.