DIY Magnetic Algae Scrubber – the ‘Spiderman Scrubber’!




Introduction: DIY Magnetic Algae Scrubber – the ‘Spiderman Scrubber’!

Hello Everyone,

After getting sick of cleaning algae from my tank having moved house to a high nitrate area, I decided to build an algae scrubber for my brackish setup. However as I don’t have a sump or room in my hood I decided to create a light that attached to the side of the tank. As I didn't really want to permanently mount anything to the glass, I came up with a Spiderman inspired algae scrubber that is mounted by magnets. After getting some good feedback from other aquarists I thought I would post how I did it.

Bill of Materials (and UK sources)

2 x Plastic Trays (I used Small Garden Trays, but anything similar should do the job)

Available – Any Garden Centre – I found them just lying about the garden - Obviously clean them first.

1 x Constant Current LED Driver – The one I originally used was 600mA however I swapped this out for 300mA as I felt it would be plenty bright enough at lower currents. It also produced less heat so made sense. Note that for all power LEDs you need a constant current source rather than normal DC switching supplies. These aren't that expensive any more and the ones I used come with a 5 years warranty. NICE!

Available at - here

10 x Deep Red (640 – 660nm) 3W Power LEDs.

Available - here

These are the work horse of the project and man they are bright. I opted for these EPILED 3W as they were a great price much more powerful than the standard non-brand stuff you find on ebay. Again seller offers a decent 3 year warranty (although doubt dropping in aquariums is covered!) Still nice to know! .

1 x Sheet of Aluminium Big enough to cover the bottom of the trays

Available at -

Again great seller, and cheapest I found at the time, came within a few days and wasn't that expensive and did the job great. Would use this guy again for sure.

2 x Plastic Knitting Canvases

Available at -

Again great seller, cheap as chips and arrived next day!

1 x Tube of Aquarium Sealant

Available at -

Whilst Pets at home are useless for fish you can't really complain at their dry goods prices, not even online. Check stock before you go though.

1 x Tube Thermal Glue (10g) – you don’t need much so 10g should be plenty for 10 LEDs

Available at -

Small section of L shaped Alluminium Extrusion alternatively you could use small brackets

Available at any DIY/hardware shop – I had mine just lying around after my neighbour dismantled an old greenhouse

2 x Large Aquarium Algae Magnets (need to be as large as possible but must fit inside the plastic trays. Also they need to have flat edges for attaching various things to. I suspect this is an area that I could improve the design upon but was all I could find at the time.

Available -

Machine Screws (M3 or M4 machine screws and Nylon Lined Nuts)

Available at –


Total Cost for all these was around £30 which seems pretty reasonable seeing as the cheapest algae scrubber I could find was at least double this and had nowhere near the power.

* Cautionary note!!

It goes without saying that electricity and aquariums don’t mix well, so anyone who is inspired by this posting does so does at their own risk and these instructions are provided for information purposes. The author assumes no responsibility for injury or damage to equipment resulting from information provided in this post. The article is provided from information purposes only

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Step 1: Creating the Scrubbing Plates and Housing.

*I thoroughly recommend doing this section first as the silicon sealant I was using took 48 hours to cure. It makes sense to complete the other sections whilst you are waiting for the silicon to dry.

1. Cut the Plastic Knitting Canvas to size using ordinary scissors. Make it so that it fits snugly in the bottom of one of the plastic trays.

2. Repeat this with the second canvas and make sure they both fit neatly on top of each other.

3. You now need to mount the bottom half of the aquarium magnets to the tray you want to place inside your aquarium. Using the silicon sealant glue the inside parts of the magnets to the sides of the plastic tray. In order to give extra stability I used an L shaped piece of plastic glue to the rear of the magnet to create more surface area to adhere to.

Once you have done this you need to let the sealant cure for 48 hours (if you used the brand I did – I am sure there are quicker drying brands out there).

I left mine face down on a flat table top after holding it in place for a while by hand. It might be worth using small plastic clamps at this stage, although my method seemed to work just fine. The scrubbing plates and housing are now finished. Whilst it is drying I got on with building the lighting platform

Step 2: Building the Lighting Section and Housing

1.Firstly take the Aluminium plate and check that it fits inside your plastic tray with some space around it. If it needs trimming this is easily done with a hack saw.

2. Look at the rear of the plastic tray and see if there are any grooves that the tray might sit on. If so cuts these out using a Stanley knife. You should be left with a tray with two neat slots down the rear. These are where you heat sink fins will protrude from.

3. Next cut two sections of aluminium extrusion to the length of slots. Measure out the positioning of the slots onto the plate and mount your two sections of extrusion so that they align with the two slots. This is done simply by drilling 2 holes at either end of the extrusion and through the plate. NOTE – THESE Holes should be some distance from the vertical part of the extrusion angle so that they can be pushed through the back of the tray through their own holes and NOT through the slot. These screws will act as the fixings for you plastic tray to the light so this is quite important.

4. Thread through 4 x M4 screws so that they extend from the same side as the fins. Now drill 4 holes in the back of the tray that align with the screws you have just fitted. You should now be able to mount the plastic tray neatly onto the rear of the aluminium plate with the two fins and screws protruding neatly through their own holes.

Step 3: Putting the Platform Together

5. You now need to attach the plate to the two magnets. This is done by simply screwing a piece of L shaped extrusion directly into the top magnets. Here I simply drilled to small pilot holes one through the extrusion then one into the magnet itself . Two self tapping screws where then screwed into the magnets holding the extrusion in place.for extra stability I added a little of the silicon glue. I suspect an epoxy glue would be superior glue here I had loads for mounting the high power LEDs.

You then need to attach another section of extrusion to the piece you have attached to the magnet. This is done by drilling two further holes through each piece and bolting them together using the m4 screws and nuts.

6. You should now have magnets with two small platforms from which the main plate from earlier can be mounted. However before you drill the holes to mount the central plate you need make sure the position of the magnets in each tray align perfectly. Here you need to take the other tray (once it is dry) and measure exactly where the magnets on the inner tray will meet the outer tray. This is done by simply aligning the two trays next to each other and marking with a pen on the inside of the tray where they will meet. You then attach the main plate to the outer tray once again so that the fins extend from the top and mark where you need to drill the holes, so the magnets fall in line with the two marks you have just made on the inside of the trays. You then mount the central plate to the two magnets with m4 screws and bolts as before. Once the whole thing is bolted together it should look something like the picture above and fit neatly inside the box.

7. At this point I did a sanity check by mounting the two pieces onto a house window to check it all met flush on both sides and the two trays aligned perfectly.

Step 4: Mounting the LEDs

1. Finally you just need to add the LEDs to the central plate. This is done by simply marking out a pattern for the 10 LEDs then gluing them directly onto the aluminium using thermal glue. NOTE – THIS MUST BE THERMAL GLUE AS YOU NEED TO DISSIPATE HEAT POWER LEDS CREATE AS BEST YOU CAN TO ALLOW THE FINS BEHIND TO WORK. Allow the glue to dry – this is quite quick (probably as little as a couple of hours if you are using a silicon type (check the label!)

2. Next cut pieces of wire and solder them in between each LED. As I was using a constant current driver which adjust its voltage automatically this was simple just requiring one series circuit including all 10 LEDS. I also added a quick blow 700mA fuse at this point just to give a bit of protection to the circuit in case of failure, although the circuit will of course work fine without.

3. Next you just need to wire the output of the LED driver to the + and – sides of your series circuit as per the simple schematic. You then need to wire the driver to a plug and maybe a switch if you plan to turn it off manually. MAKE SURE YOUR LEAVE ENOUGH CABLE SO THAT THE DRIVER IS MILES AWAY FROM ANY WATER!! YOU MIGHT ALSO CONSIDER MAKING SURE THERE ARE NO EXPOSED CABLES ANYWHERE.

4. Turn on and test circuit. * Beware the LEDS are VERY bright be careful not to look at them directly as they could easily damage your eyes.

Step 5: Installation of Lighting and Algae Trays

* AGAIN - Make sure your light is UNPLUGGED! and the drivers is MILES away from any water. Whilst the voltages and current of the drivers output are very low the input is mains power so be careful. As I said before this is a prototype for development purposes so read with caution.

1. Place the two plastic canvas sheets inside the internal tray with the magnets glued to the edge and place on the inside wall of your aquarium.

2. Align the completed lighting module with the tray on the inside of the aquarium. Hey presto the two pieces will stick hold firmly on the glass without any problems at all.

3. Making sure that the driver is safely away from the tank. Turn on the unit and leave it on for as long as possible during the day (I actually keep mine on 24 hours!). This will cause a huge amount of algae to form on the canvas sheets. After a few days check its progress it took me a few week to build up a decent coverage (see photo above).

When the sheets are covered simply TURN OFF THE UNIT and remove the lighting side from the aquarium remember these are magnets if you take the inside out first the other side will fall off!

Next remove the algae tray from the aquarium and rinse the sheets to get off any loose algae. DON'T Scrub them as you want to retain a nice thick layer to keep the algae growing quickly after water changes. It make take a while for the algae to start growing at first but when it take hold you should see the nitrate levels shoot down and everything else in the tank should remain virtually algae free!

Happy days!

Step 6: Design Improvement??

If you feel like this post has been useful or feel that there are improvements to be made, please feel free to post below. As I say this post is provided for information purposes only to help provide inspiration for new ideas and better DIY designs. There are plenty of things that could be improved with this project, however as a prototype 1.0 it has worked pretty well. The deep red LEDs are ridiculously bright and worked an absolute treat and have kept my aquarium very clean. I will keep improving this as a concept until I get to something better. Things such as light leakage around the edge of the plastic boxes is still something of a problem, however I suspect some kind of window seal will solve that.

I feel like adding some kind of air pump would be useful and the trays are probably far to large for most peoples tastes but as an idea I think it has legs! I hope someone finds this use and welcome suggesting and improvements to the design!

Thanks for reading


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    8 Discussions


    2 years ago

    Very clear and helpful and exactly what I was after. I built and ran a different type of DIY scrubber for several years but it was taking up too much room in my sump so decided to build one like yours. Sadly I used some LED strips which are not that strong so rebuild the dry side.


    Reply 2 years ago

    Thanks! Glad someone is still finding this useful. LED strips arent going to be that great. Using power LEDs was definitely the way to go although there are a lot of very dodgy suppliers out there. I would really recommend using a decent one with brand name chips. The suppliers I used here I have used for quite a few projects now and they are always great and none have failed since I wrote this in 2015! Really can't complain with that


    Reply 2 years ago

    Well, after much research on the electrics part of it, I finally build my improved dry side. Used only 4 x 3w deep red LEDs but it seems more than bright enough. I didn't use magnets like you as I didn't have any at the time. Instead, the wet side is attached using suction cups but more importantly, it's a tight fit inside the sump so it won't move when the suction cups stop working. The dry side just sits on the outside. Wish I had added a switch on the cable somewhere as this is just plugged into a timer which is hard to reach and unplug so might look into that. Thanks again for the instructions!


    Reply 2 years ago

    Sounds great! Are you planning on posting the build on here? Sure lots of people would like to see it?!


    Reply 2 years ago

    Could have done but didn't take enough pictures. I did a post on Ultimate Reef for my first scrubber but couldn't be bothered to do with this one.


    Reply 2 years ago

    Arhh ok, sure it looks great!


    Reply 5 years ago on Introduction

    no probs, let me know if anything is unclear