over-crowding/Tunnel

Question
Hi Jamie,
I have a 40g tank with 6 serpae tetras, 8 red eye, 6 black widow tetras and 6 zebra danios and a cat fish.
Q1. is the tank over crowded with that amount of fish?
Q2. I am considering a Tunnel beneath the substrate,will this effect the bio-cycle? will it benefit my fish?

Thanks

Answer
You tank is a bit crowded for my taste, but if you do 50% water changes weekly, you should be ok.  What kind of cat fish do you have?  This will make a big difference on the bioload depending on the species of cat fish.  I don't know how a tunnel would effect the biological media.  I don't know about how it would affect your fish either, I have never worked with a tunnel before.