One modification that some people are interested in for the Fluval Spec aquariums is to add a cover over the overflow slots that lead into the filtration systems. This can be useful for those wishing to breed shrimp or fish and want to keep those critters out of the filtration system. It may also be beneficial for owners of betta fish who’s long fins can get caught and torn in the return slots.
I had thought that the best way to obscure the openings would be to affix some sponge blocks over the edge to cover the slot. I never have gotten around to try this; I think the resulting piece would be difficult to keep in place and wouldn’t look good. I found an alternative in a Spec Mods forum to use stainless steel mesh as a cover over the return slots. This seemed like a good solution and one I wanted to try out.
The good thing about this mod is you can make it yourself. The slightly tough part is finding the stainless steel mesh material, but I will discuss that more below. Another plus is that a stainless steel cover will be reusable; it is durable and rust resistant so you don’t have to worry about it wearing out like a foam piece would.
Materials – Where to Source Stainless Steel Mesh:
Stainless steel mesh is available in differing opening sizes. This is designated as the mesh size, which is the number of openings per inch. 10 mesh has 10 openings per inch; 50 mesh as 50 openings per inch. For our application, we want a balance between a very fine mesh (small openings) that will be soft on fish fins and keep out the smallest of critters and a more coarse mesh, that will be stiffer (easier to work with – more durable) but would let in very small criters.
The tipping point seems to be around a 20 mesh, which is what I bought and will recommend. Look for a stainless steel type of either 304 or 316; either will resist rust and corrosion, but the 316 is slightly better in this regard.
There are many sources for stainless steel mesh online. I got mine from Amazon: Stainless Steel 20 Mesh, 15 cm x 15 cm.
Here is what you will need to make your own return slot cover:
- (1) piece of stainless steel 20 mesh, at least 10cm x 10 cm
- A pair of scissors
- A Ruler (I prefer metric for the scale of this work)
- A straight edged object with a thickness of around 2mm (such as the back of a large kitchen knife)
- Optional: bench vise
How to Form the Stainless Steel Overflow Cover:
The concept is simple – you just need a flat piece of the stainless steel mesh cut to size to cover the slot openings in the overflow. The design is to cover one side of the slots and have a small piece overhang the top and the other side to hold it in place. (never mind the shrimp inside the filter section in the photos – they snuck in before I got the screen in place!)
The good news is the stainless mesh is easy to work with. It stays fairly ridged as you bend it, but it still holds its shape. You can cut it with scissors. The mesh forms a very nice grid that is easy to follow along for a straight cut.
Step one is to cut to size to cover your slots and allow for a bit to go over the top. I cut mine (for a Spec V aquarium) to 95mm wide and 55mm tall.
Once it is cut, you need to find a way to put the bend at the end to hook over the top of the return slot baffle. You could just bend it right over the aquarium baffle to form it, but the forces might cause you to damage your aquarium. Better is to bend it around another object of about the same thickness as the plastic of your aquarium filter baffle.
I measure the overflow baffle at around 2mm thick, so any straight object of around 2-3mm thick will do. I found a good kitchen knife with a flat back edge that did the trick.
Since I have available a bench vice, I used that to put the final squeeze on it to form it around the template.
See the photos below (click to enlarge) for dimensions of where the bend is located:
The dimensions shown are for a Spec V. I have also confirmed that these dimensions will also work with the Spec III. It is not an exact science as I just designed it to overlap the slots by 5-10 mm.
Installation and use:
It’s very easy to install; just hang it over the edge. You can have it either with the main cover inside the display tank or inside the filter section.
Water still flows freely through the mesh and doesn’t affect filtration negatively at all.
If you bend it correctly, it stays flat to the baffle and doesn’t allow critters up into the edges.
The photo above shows the overhang in the display section and the stainless cover inside the filter section. I found it a bit difficult to get the mesh inserted down next to the sponge filter and I think I prefer the opposing mount with the mesh inside the display tank. However, the tight fit against the sponge might ensure that nothing can get in; there is sometimes a gap between mesh and filter wall with the mesh installed in the display tank.
While the mesh is a metal, it is fine enough to be soft and will not cause trouble to fish fins if they brush against it. I have only had it in place for a short time, but I have not noticed any corrosion, which would be unusual to see from 304 stainless steel.
This is a Spec mod that does involve a bit of handiwork to fabricate, but I think many people would be able to do this themselves. My use of a bench vise helped greatly to get the bend nice and crisp and I think this really helped the cover stay flat and clean.
For those that absolutely want to keep fish fins, shrimp or fish fry, adult shrimp, or snails out of the filter section, this is a great mod. I went through this process to try and help those out with this need. However, I don’t expect the cover to be a permanent install in our tank. I don’t have a fish species that is bothered by the overflow slots. I also don’t care about shrimp getting into the filter section. It doesn’t ever seem to do them harm, even baby shrimp. They seem to always make their way out and are safe.
However, if you are one that has need for an overflow cover, I hope this helps you out in your planning and execution. You may even use this to come up with a better solution – let me know!
Edit: Since I first wrote this, I have found another very useful reason to keep this filter cover on our tank. When I trim our plants, especially the very small leaves on the HC Cuba, the tank can get flooded with plant bits. Having this in place helps prevent many of those bits from getting into the filter section. For the days following my trim, I daily turn off the pump, remove and wash this screen (to dislodge the plants that are built up on it), then replace. In a few days and a few cycles of cleaning, the plant bits are removed from the tank and the filter section stays clear.
41 thoughts on “How to Make a Stainless Steel Overflow Cover for Your Fluval Spec Aquarium”
Hi! Your site is awesome. I was wondering whether or not this size would be able to block baby shrimp from being sucked through. It seems like the holes are still a little too big– have you found this to be a concern at all? Would finding a finer mesh really present a large issue to constructing the cover? Thanks for your time!
You can use a finer mesh if it makes you feel more comfortable and I don’t think it would restrict flow too much. However, I have had many generations of shrimp in this tank so I see how small the fry are; I don’t believe there is any way that baby shrimp can fit through the openings of the mesh pictured (20 mesh).
Basically, 20 mesh works and smaller opening mesh (30, even 50) should work as well.
Thanks for your reply! I’ll take your word for it! =].
or you can just use this little guy! it acts like a surface skimmer!
Great blog! I like all your Ideas! you have helped me a ton.
Dan, I take it you have used the product you link to. Does it work as they say?
So in your experience you don’t need a overflow over when breeding rcs?
That is correct. I don’t know if I have ever lost any babies in there, but they breed just fine without the cover. I occasionally see them inside the filter section feeding at the top of the sponge, but I don’t get an indication they go further down or that they can’t get back out.
I would first like to thank you for this awesome blog. It has helped me a lot with setting up my Fluval Spec safely for my Betta.
He has recently taken a liking to hanging out next to the overflow cover so I’m currently trying to decide between using aquarium sponge or the stainless steel mesh. I’m leaning more towards the stainless steel mesh cover, but I don’t want to get something that could cause more harm than good. Did you test the edges of the stainless steel after cutting it to see if it would snag delicate fish fins (ie: running against pantyhose)?
Yours is a good question. There can be a bit of a rough edge where you cut the stainless mesh, something sharp enough to snag. I think there would be a way to burnish that edge with sandpaper to make it smooth; however, if it is a concern then going the sponge route might be the best.
A bead of silicone works wonders. Cutting a small piece of the lower “slit” in the tank and using silicone to keep it in place, as opposed to sealing it completely, works. The tank still looks stylish and if you smooth your silicone, it looks even better. This, of course, makes it a semi-permanent fixture. Since I have no plans to use this for anything other than a betta, I’m okay with that.
This is an awesome mod, worked great for me! Thanks for the tip.
Question, I recently pulled my off because i noticed a bunch of algae growing on it. Is that normal?
I haven’t used mine long enough to collect algae, but anything that stays in the tank, with enough light, will grow algae. Should be easy enough to brush off.
Great site – I found the edges were a little sharp – i ran a bead of epoxy along the edge and then sanded back. seems to work well
That’s a great idea for dealing with the unfinished edge of the stainless mesh – thanks for sharing!
Great post and comments!
We just added two CRSs to a Spec XII and darned if one of the little guys didn’t climb through the overflow right before our eyes. The only surprise was that it took him a day to find it.
Thank you so much for the ideas and information. We’re going to create/add our own overflow cover, as described above, and will comment again if we have any experience that might be helpful. Thank you!
I have a Spec V on its way to me.
What would you think of the idea of using some nylon screen mesh and gluing it over the openings? Hardware stores sell this to repair window and sliding door screens.
That could work; good idea – go for it!
I did what I suggested. I bought 6″ of 24″ wide screen for $0.36 and some silicone aquarium sealant. I cut a couple of pieces off the screen to size. I put some sealant around the edges of the cut pieces. I put a baggie on my hand to keep off the sealant. Then I put the screen on the Spec V vents, getting the sealant to squish up thru the screen and over the edges of the screen so no screen edges protruded. Some sealant did get on the glass. When it dried I used a razor to scrape it off.
It came out pretty good. The screen color is a little off from the wall, but not too bad.
Note the sealant has a pretty strong odor. Make sure you have ventilation.
I have some photos if there is a way to upload them.
I’d actually like to see this idea in photos. If you could, send to my email at
I have a very small 2.2 gallon and would like to get this tank and do the mesh method, but I would also like to glue the mesh on the bottom slot instead of sealing it, as I don’t want to worry about water not being able to pass through. It’s going to be a red cherry shrimp only tank, and I’m loving all the reviews and mods Nate has done, literally the best and most helpful site ever!
I just emailed photos to you, 2/13/2017 3:30PM Colorado time. Let me know if they don’t show up.
Just finished making this overflow cover. Thanks for the detailed instructions!
This mod upgrade is most definitely NOT required for a betta!! With 50 years experience raising bettas; I can assure all that based on my contacts with FLUVAL, this upgrade is only what someone else feels is required!! The mesh screen offered actually restricts flow into the filtration compartment, etc.,etc! If your raising shrimp it’s OK; but your still restricting flow into the filtration compartment-Believe it , or Not!
I appreciate your comment. I don’t keep betters and am only posting this as a mod that some people want. It’s most useful to me after I trim my plants to keep cuttings out of the filter section.
Though it may not be necessary for all bettas I think it is a very useful mod and one that I’ve been looking for. My betta has SBD as a birth defect, he basically always suffers from it and has a lot of trouble unsticking himself from the intake on my filter. I will be trying this method ASAP and hope it reduces the flow enough that he no longer has this problem.
Great idea! This might not work for baby scimps… but it works great for my beta who loves to sleep on the return. It’s a the black plastic mesh used for needlework crafts. Just cut it along the grid to size and attach with two small black zip ties.
Hi, I have found a very easy, cheap, effective way to solve this problem while also adding other benefits in the process such as adding a more coarse layer of filtration at the top to catch the bigger particles and allow them to break down before getting to the main sponge. It is also great for shrimp to graze on. Also I have never seen even a newborn dwarf shrimp be able to get through it and make its way into the filter section. It fits perfectly and rarely ever needs cleaning (in my experience). Another bonus is that it is completely hidden.
Here is the link:
It is a sponge filter for a fluval aquaclear 30, it comes in a 3 pack so you will have enough to last a very long time.
This fits all of the spec tanks that use the same size sponge as the spec III and spec v.
Also as added filtration, underneath the big foam block, I use a filter floss sheet and cut 2 pieces to the size of the compartment and stack them on top of each other. You have to cut it pretty precisely to make it sit on the tiny shelf so it doesn’t fall down when you put the foam block back in.
I hope this helps everyone.
I now do something similar – I have a polishing pad (bottom) and some two-layer filter floss pad on top. Keeps shrimp (mostly) out and adds a great deal of filtration! I will be writing about this soon.
Do you sell these?
Any idea for covering the small single vent at the bottom? I cant stop shrimp from going in either one and they never get back out on their own.
No. I don’t sell these. Check this page (and the comments at the bottom) for ideas on plugging that bypass slot.
Thanks for the good fix for my Spec V. So how to you finish the edges so that the sides don’t snag his fins? My betta just flattened himself of there and if there and I imagine it can catch on the unfinished edges. Thanks in advance for your thooughts.
You might try laying on a bead of aquarium silicone on that edge.
5+ years later, so not sure this will be seen. I received a large sheet of this mesh and am wondering if I can cut a tall sheet to fit inside the entire back wall? I would create the top fold as seen in this post but the portion inside the tank would go further down to also cover the smaller intake hole. The large sponge block would ideally hold it flush against the wall. Of course I already have shrimp in my Spec V so this limits what I can do.
You could try. However, I’d envision a problem with the filter media (sponge) getting caught on the mesh as you slide it down into place. The smaller version I build on this page slides into place after I put the filter media in.
Give it a shot – I’ve never tried it that way so I can’t say for sure your idea wouldn’t work.
Has anyone found a 3d printer file for this type of shrimp guard for a Spec v?
I am actually working on a 3D printable design at the moment that is very similar to this. There are some designs out there that are very blocky and use a lot of material. My design almost mimics this exactly. Would you be interested in a STL or the actual guard itself?
This is an amazing mod idea. Very easy to follow the directions and cheap considering all the little guys that died because they easily fit through the stock drain. I bought two thinking I’d need to replace it at some point but it’s been two years now and no rust. I do recommend getting a aquarium only toothbrush to use on it every once and a while. Helps keep it unclogged. I use other mods in the sump area and the screen easily pops out of the way if needed but mostly never moves. Very happy I did this, I was about to buy another aquarium because I kept loosing shrimp and crayfish.
Awesome – great job saving some shrimp! Yes – an aquarium specific toothbrush is such an invaluable tool.