I built one & mine is outside also. I have a problem with mine getting PEA SOUP GREEN. Have you ever had this problem?? and what did you do to control it??
I had a similar situation and found that it was getting light exposure through some of the cracks. This was causing algae to spread in the tank. Swapping filter material, cleaning the filter bucket and treating the water with an algae treatment worked OK. I even used a Barley Straw Pond treatment ball, found on Amazon. It cleaned the water well enough to keep the fish alive but it was still tinted. Eventually I drained the tank, cleaned everything, covered the cracks and started over. Hoping you can find the right combination. Good luck!!
