It made me feel better watching my ray eat him lol.
You put alot of thought into your sump I wish I did more thinking and less doing on mine but it is what it is.
You can see in my pictures that there is a space to the right I want to use what would be your suggestion for media? I recently put snails in there but would much rather use it for bio if I can. Added a picture of my other sump aswell incase you have some input on changes or ways to make it better
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On that second sump (hard to view pic was upside down) you could totally put a bio-tower in there....even two...feed it with the water that is in the sump with a small submersible pump and keep it on a separate switch so it circulates when the return is off...like during a water change.
If you would like to know how to build a bio-tower I would be glad to guide you....they are very easy...and you can make them cheap...