Fish water turned black?

andwhatnot.

New member
The past week I've been away on vacation and left my dad to feed my beta fish. I came home to a dead fish and pitch black water. He said he feed it everyday but being a guy he wouldn't dare to clean the water. My fish tank has (fake) plants coming out of the top and air holes. I noticed my dad had blocked off some of the smaller air holes leaving only one that is about 1/16th of the top opening. What caused the water to turn pitch black?
oh and I don't have a filter. I've have many fish before and have never had a filter before with no problems.
 
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