Haha it’s an 60cm x 60 cm x 60cm acrylic box that’s meant to replicate small-scale offshore conditions for a wind turbine foundation to install into the sand

Hi all! I’m trying to identify what’s growing and how to get rid of it since we’ll have students digging around in the water and play sand. I’ve tried adding pool shock but as you can see it didn’t work, maybe bc the shocked water didn’t penetrate the sand. If you can point me to a subreddit that may have experience with something like this or if you have any info that may help would be much appreciated!

Take my upvote for spelling titanic with Cyrillic