Algae or dirt?

[FernTheBrute]

I have little pile up coming back almost every two days. Zoomed 5x from surface of my above ground pool.



The bottom of my pool is pretty uneven so they tend to accumulate pretty much always in the same spot - at the bottom along the wall where my return is located and near the opposite wall (oval pool). As you can see it tends to get stuck on a liner seam (2nd pic) among other places. Due to return placement and pool shape, I'm not getting a good circulation in that pool and I might have a whirlpool making stuff sink in that spot over time. There is nothing of that kind near my skimmer and around where it feeds itself, only where the return seems to push water.

When brushing it, it doesn't seem to make a colored cloud like green algae does. I'll push it to my bottom drain but it will come back. It's usually worse if I let the filter run 24/7 like I do know because of the near-freezing temperature nights.

It's only on the bottom of the pool, nothing on the walls themselves.

All seems to point out to dirt because of its placement, but I want to make sure I'm not dealing with anything nastier like mustard (does this even grows in cold climates like Quebec, in below the 60F water?)
Thanks!

 

[reggiehammond]

The best way to confirm algae is to not guess, but to use an Overnight Chlorine Loss Test.

TFP principles rely on self-testing. Do you have a proper test kit?
Test Kits Compared

 

[FernTheBrute]

The best way to confirm algae is to not guess, but to use an Overnight Chlorine Loss Test.

TFP principles rely on self-testing. Do you have a proper test kit?
Test Kits Compared

I don't. Started the TFP process late in the season and the Taylor 2600c test kit takes forever to deliver to my home (canada), I've decided to wait until spring to get one. Since every test kit I have stops at 5, it's a bit hard to do. That said, I add minimal FC (compared to summer time) since the water is freezing cold and it's level seems to keep rising.
Had the same deposits all summer long.

 

[reggiehammond]

Ok, understood. Without knowing your actual FC level and CYA level, you'll struggle to know what level of FC is necessary to stave off algae.

FC/CYA Levels

Water can be pretty clear, but still have algae, and what you're seeing is fairly consistent with that. As the water gets colder, the algae will go dormant until water temps rise, so you can wait until Spring to deal with it.

 

[FernTheBrute]

Ok, understood. Without knowing your actual FC level and CYA level, you'll struggle to know what level of FC is necessary to stave off algae.

FC/CYA Levels

Water can be pretty clear, but still have algae, and what you're seeing is fairly consistent with that. As the water gets colder, the algae will go dormant until water temps rise, so you can wait until Spring to deal with it.

Yeah I know at what level my cya is (45-50) and what FC level I need to aim for (6-8), I'm just eyeballing it with an approximation based on a few drop tests and pool store tests done at the same time. Terrible to do a proper SLAM or test FC loss, but good enough to get me to next week.

Had some green algae early in the summer when my cya got too high (before I switched to TFP method) and it gave a green hue when brushed, which this deposit doesn't. The fact that it get worse with more pump and filter use and is very localized is a bit special.

Also forgot to add to my initial post that it's only located on the bottom, there is nothing on the walls.