I went back and looked at pictures of the pool with live algae and now that I look at it a little more I think what I'm seeing might still be the real thing. Just surprised it's not eating up more FC than it is... Last night FC was 6 before going to bed last night and it was still 6 when I checked this morning. I'm using Trichlor in a floater since the previous owners left a huge bucket full and my CYA is <20.
This was the swamp we started with:
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We drained down to a foot of nasty water. Got out as much organic material as we good and did a refill. This was our results after the first night of SLAM:
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What I'm seeing now looks a lot like that except in just really small patches around the bottom.
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Here's what it looked like about two hours after brushing. Color is kind of wild looking ... sun was REALLY bright.