Join Date: Feb 2012
Location: Ontario, Canada
It's up to you for the HOB, I'm not too sure if 2 sponge filters for a 20G tank will be enough or not. But I'd certainly love to know how it goes. I recommended it only because you have it, if no other filtration will be available I still think adding it is a good idea.
The two months I recommended includes the patience implicitly ;-)
PS: adding tons of moss does look good, but they become a problem when you need to net a specific shrimp from the tank. The one you try to catch is always THE ONLY ONE that will hide behind/under moss/DW.
PS 2: unless you use very little ADA or start with matured filter, I don't think 1 month cuts it for cycling ADA. I have a 10 G tank set up with ADS New Amazonia on December 13, and it's still leaching ammonia last night.