Automatic mechanical filtration
An automatic mechanical filter provides all the benefits of running filter socks, but removes particulates before they can break down in your tank and increase nitrates, and only needs to be changed once a month or less- depending on design. The basic design is a supply role of filter media, and a spool driven by a motor that takes up used filter media. Bulk Reef Supply sells the Rollermat for $400, which is similar in function. I don’t like the design of the Rollermat, but it’s an OK off the shelf option. This DIY tutorial will show you how to make an auto filter that is inexpensive and compact.

Here is a video of the auto filter in action.

And here is how to make it:

Tools needed (ish):
Table saw
Drill press
Router (not really, but if you got ‘em, smoke ‘em!)
Sewing machine (depending on filter media)

¼’’ plexiglass- free, I’m a closet hoarder and someone was throwing out large sheets. Price is highly variable, but should be cheap if you find a good plastics supplier, i.e. don’t use home depot.
Silicon- $5
Acrylic cement- I used scigrip 16- $6 on amazon. Those who are better at acrylic fabrication may want to use a less viscous cement.
PVC pipe of various diameters-$5
Power supply- free (we’ll say $8 for the non-hoarder)
Switch- $5
Timer or float switch- $16
Pulley or gear- $5
Gear motor-$12-25 for the non-hoarder

Drip Plate:
This is not a real drip plate, since it will be submerged in your sump, but the idea is the same. I made mine out of ¼’’ plexi. Holes are spaced randomly approximately 1/2 inch apart. I used a ¼’’ drill bit and chamfered the holes on one the filter side, although this is not entirely necessary. I can’t find a good off the shelf option, but if someone knows of one please comment where to find it. This plate can also be positioned horizontally if space is not a problem

Filter media guides:
I splurged here and mostly used plexi rod ($7 on ebay). You can just as easily use pvc. ½ ‘’ diameter seems to work well. I siliconed mine in place ¼’’ away the drip plate. Depending on filter media this dimension might have to be more or less.

Filter Housing:
I used ¼’’ plexi. My housing is designed to fit on a 40 gallon breeder sump. My sump must be under my tank, and I have limited clearance (about a foot above the breeder), so my housing is side loading. The spool holder is held in place by the front panel, which is held in place by ¼’’ nylon bolts. For the various holes needed, drill slowly, and use a hole saw for holes over ¼’’. If you run a sump outside the stand, I highly recommend having the spools load from the top, as this simplifies construction and maintenance. The plate that holds the motor can be taken out the top of the housing for servicing.


Motor and electronics:
I used a gearmotor that I had lying around from a medical dosing pump, but any low RPM motor should work just fine. Gearmotors can be bought for less than $15 on ebay if you want the more durable solution- they use a high rpm motor and step it down using gears.
Here are 2 examples from ebay

A pulley or gear with a set screw. Must fit over the motor spindle and inside the pvc pipe you are using as a spool ( I used 1.5’’) - I found a pulley at my local hardware store and removed one of the side guides, but McMaster-Carr and ebay carry all sorts if you can’t find one. 2 part epoxy or other cement the pulley into the pvc spool. (the picture shows me using silicon- which eventually failed)

I wanted to be able to reverse my take up spool so that I could easily unload it, so I used a double throw, double pole switch from my local hardware store. Wired like this:

AC adapter- most dosing pump motors are 12 volt

You will need a way to control when the motor advances and the spool takes up filter media. The Rollermat uses a float switch, and advances the spool when the media begins to clog and water level rises. This is probably a better option if you use a very fine filter media. If you go this route you can just wire the float switch inline between the switch and motor. I didn’t want to leave detritus in the tank that long and am using a 200 micron filter media, so I chose to use a timer instead. The downside to this method is that less material is exchanged at the beginning of the spool than at the end- i.e. the circumference of the take up spool changes. You can mitigate this by using a larger spool. You need a timer that can be programmed for a certain number of seconds, or a tank controller. I found this timer off amazon: Digital Programmable Timer Socket Plug Wall Home Plug-in switch Energy-Saving Outlet - do an amazon search- apparently I can't link. I now have an apex, so I use that, but it is really just a glorified timer.

Filter Media:
There are multiple options for filter media. Anything that can be used to make a filter sock will work. The most economical options are batting (approx. 200 micron), milk filter paper (approx. 35-50 micron), or coolant filter paper. I bought 7 yards of soft and bright for $30 at the fabric store, and sewed two lengths together for 14 yards, with enough material left over to make two more spools. This material is not indestructible, so use a laundry bag when you throw it in the washer to clean it. For a disposable option, milk filter paper can be bought as case of 6 12’’ by 200’ rolls for $140 online or coolant paper is $30 for 400 ft. If you changed a foot a day of milk filter paper, that is enough to last more than 3 years. Lastly you need a way to attach the media to the take up spool. I sewed two straps to the batting, and threaded them through 2 holes in the pvc I drilled. If you are using paper then a single hole that you pull the paper through would work well.

That’s it!