Algae doesn't seem to be going away

[phuman4]

Hi,

I "reopened" my pool probably around 6 weeks ago and it was completely green (even had some living things swimming in it!). I started the SLAM process and have kept very high chlorine levels without any CYA added (CYA below 20). The only step I didn't initially take was to adjust pH levels.
Today it's night and day, the water is very clear.

However, while the water is very clear for the past week or two I am seeing a persistant small amount of algae on the floor. I've added photos to show this. It comes back after being vacuumed or brushed. I have been running the vacuum every other day.

It's been hot the last few days so I finally added instant conditioner to bring CYA up (yes, I know I probably wasted money on having to add extra chlorine without the CYA before this).
I also thought the reason for the SLAM taking so long is that I didn't initially adjust pH levels. I let FC fall below 10 and yesterday I re-tested the pH levels and added acid to lower the pH.

Today's tests are:
FC: 13
CC: 0
TA: 180
CYA: 40
pH levels (tested while FC was under 10 after adding acid): 7.4
Results above are prior to adding extra chlorine to bump up to SLAM levels.

My question is: based on the photos can you tell what type of algae this is? Is it algae or just dirt? I've also heard that dead algae could settle on the floor, could that be happening?
I'm surprised my CC is zero as if there was algae, I would have expected CC to be higher?
Do I just keep going with the SLAM process for another few weeks? It feels like I'm doing something wrong since it's at least a week or maybe two where the water is clear but I still have the "dust" on the pool floor. Most other SLAM posts appear to resolve in a few days and at most a week or so.

Photos (they were too large to upload, there are 3 photos):

https://imgur.com/a/4AOfErD

Thanks!

 

[aeh0603]

Your pool looks pretty good, but it does look like dead algae to me. You are definitely near the end of the SLAM, but not done yet. Generally when a SLAM drags on like you describe it's time to go back to the details of the process.

Are you brushing every surface of the pool at least once per day? Have you removed the ladder/stairs and made sure there is no algae hiding in them? Check any potential hiding spots for algae, skimmer/weir door, fountains, solar, any additional features you may have. Have you opened up your sand filter to see the condition of the sand? Have you deep cleaned the sand?

Have you done and OCLT? How many times per day are you testing and adding FC back to SLAM level?

 

[phuman4]

I haven't done an OCLT - I didn't think it was ready if I visually saw the algae.
I've been testing once per day. In the first few weeks (when the pool was really green), I kept the chlorine well above SLAM levels so there was no chance it would drop below SLAM levels prior to adding more chlorine the next day.

The stairs I have are hollow (and were filled with sand to add weight), per the recommendations of the manufacturer. Inside the columns that make up the stairs is really the only place I can think of that I haven't brushed or looked. Do you think this could be the culprit?
I have not looked at the sand filter, but it is both a brand new pump and new sand from last year.

 

[heikejohn]

** The stairs I have are hollow (and were filled with sand to add weight), per the recommendations of the manufacturer. Inside the columns that make up the stairs is really the only place I can think of that I haven't brushed or looked. Do you think this could be the culprit? **

YES
We weight down our steps with 2' pieces of concrete filled PVC pipes, capped off on both sides.
The sand turned into an algae sludge!!!

 

[setsailsoon]

4,

Sorry to hear you've had this problem. Looks like you've learned a lot through this episode and you're getting close. I would guess the extended time for your SLAM was more due to your low CYA but also as pH rises chlorine is less effective. So you probably had two strikes against you to start. But at least you stopped and fixed both so you should get this completed soon.

The algae in the photos looks green and if it's reappearing green I would guess it's still a living and active flora. Just stay at slam levels and continue scrubbing. At this stage with the proper CYA and FC level it shouldn't take too much longer. You should be at 16 FC and test as often as practical to be sure you don't drop below. Have you checked your filter? How often are you back flushing?

Chris

 

[aeh0603]

Only testing once per day is known to slow down pregress on a SLAM. The hollow stairs are also a fairly common place for algae to hide, so I would recommend removing your stairs to check that if you can. I also recommend that you open up your filter soon to check the condition of the sand, as that is another source known to slow down a SLAM.

Other than checking those things the best thing you can do is just keep following the SLAM process. Check and dose FC at least 3 times per day, brush everything at least one per day, vacuum as needed, backwash your filter whenever pressure rises by 25% over the clean pressure.