While it's good to be skeptical, algae tanks like this are actually a good idea for the use-cases for which they are designed. Places where trees would be difficult and expensive to grow. The tanks more efficiently capture carbon, require less maintenance, produce fertilizer as a byproduct and the solar panels on the tank produce enough extra power for there to be a USB charger on the bench. The goal isn't to replace trees with tanks but to use them where it makes sense to do so.