Dark Stains on pebble tec plaster

[mmanchester81]

Hi everyone,

There are some dark spots that have developed by our steps and near a few of the walls that I can't seem to find any information about. I was hoping someone could help me identify what the cause might be and how to treat them. I have a pebble tec chlorine pool and for the most part keep my chemicals within the proper range. There have been times where the PH is on the slightly higher side and given the Houston heat, chlorine can sometimes be too low, but other than that the chemicals typically stay within the proper ranges. I've included a picture below so if anyone has any ideas/solutioins, please let me know!

 

[YippeeSkippy]

Hey there MManchester81- Do you have metals in your water or use copper containing algaecides? Those can cause staining for sure.

Can you provide us an set of current test results:
FC
CC
pH
TA
CH
CYA

How do you chlorinate your pool? City or well water fill?

Maddie

 

[louisd1205]

I have these exact black stains on my inground pool steps and elsewhere. It is black algae. I treat it by poring chlorine granules on the black areas and watching them go away. After that, I use a stainless steel wire brush to break them up. They will NOT go away just by shocking the pool.

 

[mmanchester81]

My FC is 4 ppm right now, PH 7.5, TA 90, CH 340, CYA 80. I chlorinate my pool with dichlor tablets from the chlorinator. My pool is city water.

I'm not aware of metals in my water but I haven't ever tested for them. I have had to use algaecides with copper in them in the past. Do you think that's what was causing it?

I don't think the stains are black algae. I've used a chlorine tablet on them and they don't change, so I thought it was metal based.

 

[YippeeSkippy]

Get some cheap Vit C chewable tablets and stuff a bunch in to a sock. Smash 'em up a bit and then rub this on the stain. If it lifts it, it implies it is a metal stain.

Sadly, copper is a PITA to get rid of. Never use anything in the pool that contains copper. We don't even believe algaecides are necessary.

Take a sample of water to a pool store and ask if they'll test for metals. This is the one time we use pool store testing, just cause no one wants to buy those test kits just for one test.

Maddie

 

[jblizzle]

Yeah, that is not what black algae looks like.

FYI, the tablets you are using are Trichlor, not dichlor ... and they are why your CYA is now too high and you likely need to start thinking about replacing water. And given that the CYA is high, your FC is not nearly high enough either to keep the water clear ... see the [FC/CYA][/FC/CYA].

Note that if the stain is copper, the vitamin C may actually make it darker. If it is iron, then they will lighten.