Is this black spot

[david5]

I have some black marks on the bottom of my pool which do not brush off and I am unsure if they are black spot and how to treat.
We have had a lot of rain here since before Christmas and recently my water became cloudy (mostly white looking).

I got my pool water tested early Feb at the pool shop PH and Chlorine were good although I had to add some alkalinity up, salt, calcium and cyanuric acid. I added most of these things but I have been adding calcium slowly since it needs a lot. The water did no clear up so I used some clarifier and ran the pump for 24hrs which cleared it up quite well. I got my water tested again and this time I needed to add acid, more alkalinity up (which i have not got yet), more salt (they only had 1 bag first visit) and this time chlorine was on the high side (6.74). I have noticed there also seems to be some white sustance on the wall it is not chalky and does brush off a little but seems to settle again on the wall later. It does not feel any different running my hand over it.
The latest results show:-
Total Chlorine 6.74
Free Chlorine 6.74
Combined Chlorine 0
Salt 3364 (I have since added another bag)
PH 7.9 (I added 300ml acid)
Total Alkalinity 64 (I need to buy some alkalinity up)
Cyanuric Acid 42
Total Hardness 66
Calcium Hardness 66 (I am adding calcium slowly)
Any help appreciated

 

[david5]

Some pics one from the deep end other from middle of the pool
Sorry they are hard to see

 

[ChrisLPC]

Does it brush away? What type of salt are you using?

 

[mgtfp]

Hey Dave, looks like you turned from long term lurking to posting. Sorry to hear that you are having issues.

Can you scrape the black spots off with your fingernail? If it's black algae then it should look greenish on your finger.

Step 1: Get a proper test kit from Clear Choice Labs. They are based in Brisbane, and their kits are essential for the TFP method.

Step 2: Run a complete set of tests with the CCL kit.

Step 3: Do an Overnight Chlorine Loss Test, this will help to determine if your issues are algae based.

Don't add any Alkalinity increaser until you confirmed your actual TA level with your CCL kit. I wouldn't trust pool shop testing, particularly TA, never clear whether they report "real" total or corrected Alkalinity.

While waiting for your kit, start reading through Pool Care Basics.

And let's get @AUSpool and @needsajet involved, so you get to know more of the Aussies here.

 

[mgtfp]

What is the pool surface? Would be great if you could add your pool and equipment details to your signature.

Hold your phone landscape, then you can see for example my signature below my post as a template.