Wet Dry filters are in my opinion the greatest filters and simplest.  I will explain the basics of how wet dry filters work and how to set them up.  In edition I will explain why your wet dry doesn't overflow during a powerfailure.  A general guide to size and the steps to take on enitial set up.  General guide to help a new person. 

Wet Dry Filters are by far one of the most efficient methods of filtering aquariums.  Biological and Mechanical filtering.  The filtering capacity is not limited because you can choose the Gallons Per Hour of flow with your desired pump output.  Canister and Hang on back styles are limited GPH water flow with much less effeciency.   Wet Dry Filters are hassle free filters because the only thing you really have to do once in operation is 2 things.  First is clean your filter pad.  Second is keep it topped off with water.  It's as simple as sliding the filter media tray to the side, reach in and extract the filter pad, clean it and put it back or replace it.  You don't have to worry about bacteria being off balance because your bioballs do that for you.    When you get your filter up and running.  You will notice a water level is established in your wet dry filter.  This level is probably 1 to 3" above your water pump.  The total water height will be anywhere between 5 to 7 inches probably.  Some wet dry filters come with a water line guage.  Ignore that and mark your own water line with a piece of tape or mark a line that is permanent.  I do it with a piece of tape.
         They come in many sizes.  You need the appropriate size.  Too powerful of a pump and it will put water in your aquarium and drain your wet dry of water.  You need appropriate sump area.  Sump is the area your pump is in that holds water.  Too little amount of water and your sump is empty.   The water height of your aquarium will equelize to just above the bulkhead +/- 1/2".  Every aquarium is different because of pump GPH flow as well as aquarium height due to the aquarium stand. 
         Bioballs are really necessary for your wet dry.  Don't be fooled by other types of bio load products because the truth is this.  As long as you have surface area for bacteria to grow that handle your fish load your aquarium will have a nitrogen cycle completed.   Bioballs are cost effective and they last forever.   They are very effective at oxegenating the water and also that allows the gasses to be expelled in the water.   The nitrabacter will convert Nitrite to Nitrate on the bioballs.   Don't be fooled more is better.  Remember nitrabacter only will survive for the amount of waste needing to be converted.  You can't have a living organism if it's food source isn't available is my point.   This is why the bioballs exist.
         Water Pumps need to be sized appropriately to your fish waste load not your aquarium size.  Example is this, I had a 500GPH output at 4ft head height and my 40 Mbuna's in my 75 gallon aquarium.  When the fish matured I didn't have a turn over rate that was keeping up.  I upgraded the pump to 800GPH and my aquarium is now clean.   Basically if you have a 55 gallon with a wet dry a 300 to 400GPH pump output is good.  75 to 100 gallon 450 to 600GPH.  125 to 150 600 to 800GPH 150 to 200 800-1200GPH pump.
          How do they work.? You fill your aquarium to the bottom of the drain/bulkhead.  You fill your wet dry to approx 1-2" below the top. Turn on your pump and your done.  If your pump is appropriate sized you won't overflow your aquarium and you won't have a flooded floor where your wet dry is.  Why is this?  If you start your wet dry filter with water topped of like what is mentioned above and your aquarium is topped off just below your bulkhead drain you can't overflow your wet dry because you can't drain more water in your aquarium in to your wet dry filter.  The only way it's possible is if you put water directly in your aquraium top when your wet dry pump is on.   Water only drains to the lowest point.  So if your wet dry is topped off and your aquarium is topped off, No water is flowing in either part, how would you overflow your wet dry filter when a power failure occured?  You can't it's impossible.  Again fill your wet dry filter up.  Fill your aquarium up to just below the bulkhead drain.  The 2 water levels are set.  Turn the pump on and your aquarium water will rise until an equelibrium is established.  Water level will be just above the bulkhead.  Now turn the pump off and simulate a power failure.  What will happen?  The aquariam only drains to the bottom of the bulkhead.   This is as simple as it gets for an explanation. 
             You only need to check your water level evaperation every 2-4 days and keep it topped off.  Another great thing about wet dry filters is that your aquarium water level will remain constant.  Evaperation happens, but your wet dry filter water level will drop.  You also can keep heaters in your wet dry filter as long as your not directly on the acrylic it wll be fine.  I don't have an air bubbler in my aquarium because when the water flows through my bioballs it's creating oxegenated water.  You could put an air bubbler in your wet dry instead of your aquarium if you wanted to do that and not have it in your aquairum.  

Written by
Zak White
TxHoleyRocks
Owner