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 DIY Wet / Dry Trickle Filter By Dave R 
DIY Wet / Dry Trickle Filter
DIY Wet / Dry Trickle Filter

By Dave Rackett

Copyright, August 2002

Wet/dry Trickle filters are mainly considered to be a saltwater-type filter, but I've found that they work just as well in freshwater applications. Here's one that I built that is very simple to build and almost maintenance free.

Building your own Wet/dry Trickle Filter

This wet/dry trickle filter is a simple way to provide superior biological AND mechanical filtration. While most trickle filters only provide minimal mechanical filtration, I designed this filter with different compartments that are filled with filter floss to polish and clean the water. The results were far better than I expected. Within 30 minutes of installing this filter, the water in my 75g tank was noticeably clearer and the next day, the water virtually disappeared. It requires very simple and minimal maintenance about once every 2 months. The sizes of the parts listed will work for an aquarium up to about 75 gallons, but you may increase the size of the sump and tower compartments to provide for any size aquarium.

1- 10g aquarium for sump (or any appropriate size plastic tub)
5- plastic, stackable tupperware-style storage containers (these are at Wal-Mart and have blue plastic covers with yellow locking handles. Measuring the blue cover, I used size 9x7.)
1- 1.25" pvc coupler
1- 1.25" pvc 90 degree elbow
1- 6" length of 1.25" pvc pipe (I had to buy a full length, but it's cheap.)
1- 20" length of 1/2" cpvc (smaller outside diameter than pvc)
2- 90 degree elbows cpvc 1/2"
2- 1/2"cpvc end caps
1- 1/2" cpvc "T" fitting
1- 6' length of 1.25" corrugated vinyl hose ( like clothes dryer hose only smaller)
1- 6' length of 1/2" inside diameter clear vinyl tubing
1- Maxi- jet 1200 pump/powerhead
6- packs of plastic drinking straws
2- packs of plastic Easter grass
1- bag of polyester pillow stuffing from Wal-Mart
1- 1" thick scatchy-pad (I used a pad that goes under a floor polisher and cut it to the proper size.)
1- overflow box assembly
1- u-tube
1- 1/8" plexiglass about 9"x7"
1- 1/8" plexiglass about 4" square
1- 2" stainless-steel automotive-type hose clamp
2- 3/4" stainless-steel automotive-type hose clamps


Start by drilling 1/4" holes in the bottoms of all the storage containers except one. Space the holes about 1" apart over the whole bottom. If it cracks between holes, no big deal. It won't hurt the operation of the filter. Next discard all the blue covers except for one. In this cover, cut out the top so there is only about a 3/4" lip around the outside edge. Cut the piece of plexiglass so it is about 1/2" larger than this hole that you cut in the cover. Drill an 1.25" outside diameter hole in the center of the plexiglass so that a short piece of the 1.25" pvc pipe will just fit through it snugly. I used a drill to start the hole and then routed the rest out using a dremel tool until the pipe would fit into it just right. Then glue the plexiglass to the cover with GOOP glue. I tried aquarium silicone and it didn't hold. Wait overnight for the glue to dry. Next cut a short piece of 1.25" pvc pipe about 2" long and put the coupler on one end. Stick this up through the hole in the cover from the bottom side and put the 1.25" 90 degree elbow on the other end. Add another piece of 1.25" pvc pipe about 2" long to the other end of the elbow. This is where your hose from the overflow box will attach. The elbow and the coupler should be JUST touching the plexiglass on both sides. If they don't, take apart and shorten the short piece of pvc pipe slightly. You now have a swivel joint for the water to enter the tower. You don't have to use any pvc glue on these joints as there is no pressure here.


Now take the last storage container and cut 4" slots about 1/2" wide in the sides way down near the bottom edges. This allows the water to flow out of the tower. This compartment can be used to install activated carbon if need be, as it is always under water or you can put in more straws or Easter grass, if you'd like. I left mine empty. To fill the tower, just cut up all the drinking straws in 1" lengths and fill 2 of the compartments. Then place the Easter grass in one compartment. In the last compartment, place about 3" of filter floss and then lay the 1" scratchy pad on top of it. DO NOT COMPRESS THE FLOSS. The filter will overflow if you compact it too much. Then just lay the 4" square of plexiglass on top of the scratchy pad directly under the water inlet. This is your splash tray, it disperses the water so it doesn't flow straight down through the center of the pad.


I have stacked my compartments in the following order. Top compartment has the water inlet and floss for mechanical filtration. #2 and #3 have straws, #4 has the Easter grass and the bottom one is empty.


Do not glue any of these parts until you are finished and satified with the arrangement. Starting from the end where the hose from the pump will attach, cut a piece of 1/2" cpvc about 2" long. Place this piece in one end of a 90 degree elbow. Place another piece about 2" long in the other end of the 90. Take the second 90 and place it on the end of the second short piece and cut a piece of cpvc about 2" long and place it in the end of the second 90. Lay it flat on a table and you should have what looks like an *n*. This is what will hang the unit on the side of the tank. Then take the T fitting and place the center leg of the T on the last 2" piece. Cut 2 lengths of 1/2" cpvc about 8" long each and drill 1/8" holes down the length of each pipe about 1" apart. Place an endcap on the end of each one and stick them in the T fitting. You can leave these two legs without glue so that you can rotate the holes to direct the water where you want it. I have mine pointing down at the back glass. Now you can glue the rest of the parts so they won't come apart.



Hang your overflow on one end of the rear of your tank and attach the 1.25" corrugated hose to it. (If the fitting from the overflow box is a different size, then just get all pieces to fit this fitting. You may have to change the size of the filter tower inlet fitting also. It's ok as long as the fittings are larger than the size of the hose coming from the pump. In other words, the return lines must be much larger than the input lines to prevent the outside overflow box from overflowing on your floor.) Now place the hose on the filter tower inlet fitting. Clamp both of these connections. Put the tower in the sump if you haven't already done this. Place the 1/2" clear vinyl tubing on the outlet of the Maxi-Jet pump (remove all fittings) and clamp. Put the other end on the end of the spraybar and clamp. The filter is now ready to fill up and run. I ran mine outside using a tub up on a chair to simulate my aquarium before committing it to the 75g tank. I would suggest doing this in case you have any leaks. Your living room is the last place you want to discover you have leaks.


To get the filter started, fill up the sump a little less than half way with water. (Dechlorinate first if doing this on your aquarium). Then fill the inside and outside overflow boxes. The outside box will seek it's own level at the top of the standpipe. Then place a short length of airline tubing up inside the u-tube so the end is right at the uppermost part of the " U ". Then carefully place the u-tube into the inside and outside overflow boxes. Make sure the airline stayed where it was and didn't slip down. Now you can turn on the pump and then quickly suck on the other end of the airline removing all of the air in the u-tube. Place you finger over the end quickly to prevent air from going back in the tube and carefully remove the airline. If you don't get all the air out, it's ok as long as the bubble is not too large. If the bubble gets so large as to reach the bottom of the U, then the siphon will stop and all the water that is in your sump will then get pumped into your tank and not return. Periodically check your u-tube for bubbles and remove if necessary by inserting the airline and going through the priming steps again. It should hardly ever be necessary unless you have bubble-nest building fish, such as Gouramis or Bettas in the tank. Then their bubbles will get swept into the overflow box and accumulate in the u-tube. Watch for this. Most overflow boxes are adjustable to regulate the water level inside the tank. I keep mine right at the bottom edge of the wood trim on the top edge of the tank. The water level will always stay the same in your main tank as water is always being pumped into it. Any evaporation will occur in the sump. Make sure the water level in the sump is never high enough so that if the siphon is lost and all the water is pumped out of the sump, then the main tank will not overflow. Also, this leaves room in case the pump stops for any reason, such as feeding the fish you will want to turn off the pump, then the water coming from the overflow will stop before the sump overflows. The overflow will stop when the water level in the tank reaches the notches in the inside overflow box. If it looks like the sump will overflow, then raise the level of the overflow box. This will let less water return until the notch level is reached. The filter will restart by itself when you turn the pump back on. *VERY IMPORTANT......POSITION THE SPRAYBAR ON AN ANGLE SO THAT AT LEAST ONE HOLE IS ABOVE THE WATER LEVEL. Or you may drill a 1/8" hole in the inside T above the water level. Either way, you must have a hole above the top of the water to prevent a siphon from the spraybar back to the sump when you turn off the pump. If you don't, then the water will siphon from your tank when you turn off the pump until a hole is exposed. By this time, your sump may be overflowing. If all these precautions are followed, you should have years of worry-free service from your filter. I have had mine running now for 2 years and it has been trouble-free. I change the filter floss every 2 months and blow out the scratchy pad with a water hose. Then I clean the impeller in the pump about every 6 months. I must add that if you decide to build and use this filter, you do so at your own risk. I will not assume any responsibility for any damages that may be accrued due to the use of this filter. It uses basic theories of hydraulics in it's simple operation, but I will not be responsible for workmanship or the quality of the parts and materials used in it's manufacture. An added advantage to this filter is that you can place your heater in it instead of in the tank. Also, dosing of liquid fertilizer or medications can be put right in the sump.

Good Luck with your project and happy fishkeeping, Dave Rackett. (

Copyright 2002, Aqua Den. ALL RIGHTS RESERVED.

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