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16″ Shadow Overflow

Rated 5.00 out of 5 based on 12 customer ratings
(12 customer reviews)

$199.99 $159.99

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SKU: Shadow16 Category:



The Shadow™™ Overflow is the evolution of the Synergy Reef® overflow system. Now 100% Injection Molded! Featuring a removable weir for ease of maintenance and our molded design for fail-safe operation. Our ultra slim design has revolutionized the aquarium overflow and how aquariums get water into their filtration systems. It is a very simple to install, plug and play overflow system. Completely quiet operation when used to our specifications. Our years of testing and development are what sets our overflow system apart from anything else available.

360° view of the overflow system

Full Screen Version located Here: HD Full Screen 360º View


Up to 2500 Gallon Per Hour Flow Rates!
Front Overflow Box
16″ x 1.6″ x 5.5″ Injection Molded with durable Poly-carbonate material
2 x Removable Weir with VTeeth™ Technology ( Allows you to remove and clean the teeth of the weir)
Bulkheads are molded into the Front Overflow Box. No more separate bulkheads.
Fits aquarium thickness from 1/4″ (6 mm) up to 3/4″ (19 mm)  Glass or Acrylic tanks

Rear Box
16″ x 3.75″ x 7″ Injection Molded Seamless Translucent Black ABS
3 x 1.5″ ABS Slip fittings for easy plumbing
2 x U-Flow™ fittings that allow for compact plumbing
3 Pipe Full Siphon Overflow capability!
Removable Solid Black Polycarbonate Cover that locks into place when closed (reduces noise, eliminates salt creep and light from entering the rear box)

Please see our Q&A Tab for more information.

What are some of the key features of the Shadow® Overflow

  • Injection Molded – The obvious main change is that the overflow is now 100% injection molded. This means that every overflow will be exactly the same. Being injection molded also means no glued seams that can leak, it is truly a “One Piece” design. We are the only company that injection molds this style overflow system. Injection molding  and precision 3D CAD designed components allows us more details and features than flat stock built overflows.


  • VTeeth™ – Our new Velocity Teeth allow for an even surface skimming flow into the overflow. This maximizes the surface skimming capabilities of the overflow as the flow rate increases. This also allows us to have a very small water level differential. Injection molded VTeeth™ are smooth without any rough surfaces, this provides a continuous smooth flow.
  • U-Flow™ Pipes – Now included with every Shadow™ overflow is a set of U-Flow™ pipes. We have designed these fittings to maximize space inside of the outside rear overflow box. These compact fittings are not available off the shelf anywhere else. They allow us to fit our 1.5″ Fittings into such a small space.
  • 1.5″ Plumbing – Now standard is 1.5″ plumbing capability. No other compact overflow on the market has the capability to use 1.5″ plumbing on such a small rear box.
  • Locking Rear Cover – Our polycarbonate rear box cover is not just a rectangle piece of material. It is a feature that was specifically designed to have a function. We have designed the rear cover to lock in place when attached. It also features a channel system to keep salt creep and water inside the rear box. With design features to completely stop any warpage of the polycarbonate. No others compare!
  • Universal Fit – This will work on any non tempered glass and acrylic tanks from 1/4″ (6 mm) to 3/4″ (19 mm) Thick! Rimless and Plastic trimmed tanks all work!
  • Polycarbonate Construction – The front box and weirs are constructed out of bulletproof polycarbonate. They are practically indestructible!
  • Locking, Snap Fit Weir – Removable locking weir with our new VTeeth™ for easy maintenance and cleaning. We have designed a simple slide fit that allow for a smooth action when removing the weir in tight spots under the trim on your tank. This means ZERO Clearance is needed to remove the weir when installed under a braced tank! This is a non-magnetic locking weir design that snaps into place.

16" Shadow Locking slide weir

  • Plumb it to your needs – Rear box allows for various plumbing combinations, including the popular full siphon system. We use our modified version for full siphon. Slip fittings are molded into the overflow rear box. No more bulkheads.


Designing the overflow –

Being reef hobbyists ourselves, we spent years working on the design of this overflow. We tested hundreds of variations and options before we came to this design. Our fundamental goal was to create a low profile and quiet internal overflow box, while maintaining the flow rates desired by reef hobbyist. We wanted an overflow system that everyone would want to use. Originally we partnered with designed the overflow to be built by hand with flat sheets of acrylic. Using flat sheets for an intricate design like we envisioned was not possible. Designing the overflow with 3D software allows us to add features not possible when building it by hand out of flat acrylic. As we moved forward with the design we wanted to make a product that could be produced for everyone to enjoy. Injection molding was the answer. While it took us a long time to design and manufacture this overflow, it now is exactly where we wanted it to be.   This overflow system was designed by Synergy Reef Systems in the USA!

Manufacturing the overflow –

Injection molding allows us to make every part exactly the same. Every part is molded with the same tolerance and specification. Unlike hand build models, molding allows the Shadow to be precise in fit and form. We use the highest quality US produced Polycarbonate and ABS in our molding process. Our quality is second to none! There are lots of imitation overflows out there, but ours is the highest quality available, period!



Includes the following with the kit:

  • Front Overflow Box
  • 2 Removable Polycarbonate Front Weirs
  • 2 Polycarbonate Bulkhead Nuts
  • Seamless Rear Box with 3 x 1.5″ ABS Slip fittings
  • Locking Polycarbonate Rear Lid Cover
  • 2 U-Flow™ 90º Fittings
  • 4 Gaskets
  • Drilling Template
  • Installation Manual

This will be a self install kit. You can drill the tank and install this yourself! Instructions are located here: 16″ Shadow® Overflow Installation Manual

Drilling template is included with the overflow and we recommend you use the template when the overflow arrives to align it perfectly. But if you need the drilling template .pdf it is located here: 16″ Synergy Reef Overflow™ Drilling Template .pdf



Additional information

Weight7 lbs
Dimensions20 x 10 x 10 in

Shadow Overflow Videos

Unboxing the Shadow® Overflow. What’s included with the kit. 



How to Drill Your Aquarium and install the Shadow Overflow


Shadow™ Snap Fit Weir

 Mr. Saltwater Tank Interview @ MACNA 2016


Question: How is the 16″ Shadow different from your 20″ Synergy Overflow?

Answer: The 16” and 20” can handle the same volume since they are both using 1.5” plumbing now. The 20″ used to be the only overflow we had with 1.5″ drains, but now the Shadow also has 1.5″ drains as well. The main difference is the 20” is intended for larger builds that require glass thickness over ¾”.


Question: How much flow can the Shadow handle?

Answer: The Shadow is capable of 3000 gph flow rates. We recommend running under 2500 gph for best performance.


Question: What size tank is the Shadow good for?

Answer: So this really depends on your flow rate. We have customers with the Shadow on 15 gallon aquariums all the way up to 800 gallon aquariums. With larger systems it may be necessary to run more than one overflow.


Question: What is the largest tank for using 1 Shadow overflow?

Answer: Again this is dependent on your flow rate, but we would only recommend using 1 on tanks up to 250 gallons. The tank must have 3/4″ or less glass thickness.


Question: With the 1.5″ drains, can I reduce them down to 1″?

Answer: Yes you can reduce the drains to 1″. Keep in mind this will reduce you maximum flow rates. We recommend using a Synergy Reef Sump with plug n play 1.5″ bulkheads.


Question: It says to use either a 63 mm or 65 mm drill bit, which is best?

Answer: We recommend a 63 mm diamond drill bit for the most precise install. It will allow for less movement of the overflow when installed. 65 mm will work, but may require a little more attention when installing the gaskets.

12 reviews for 16″ Shadow Overflow

  1. Rated 5 out of 5


    I ordered the Shadow Overflow back in October from BRS and I’m loving it so far. I used it to replace my DIY PVC overflow on my 75 and it works so much better. Especially since it used a bean animal style in the back and I don’t need to prime the overflow every time it stops.

  2. Rated 5 out of 5


    Great overflow, I purchased the 16″ shadow overflow for my 120 gallon tank. The template was easy to use for proper placement for drilling the holes in my tank, and the overflow is amazing! I’ve had many comments on how nice it looks from other reefers getting frags from me, and how nice it is to have the extra space on the back wall since it discharges the water through the back. You have to set your tank away from the wall a few inches of course, but I already had mine set away because I use a led stripe to give a nice backdrop illumination between the tank and wall…..and to be able to route a new cord if needed!!
    If I’m going to build another tank I will be sure to use this overflow again, well actually I’d get the 20″ just for more surface skim area. there’s nothing wrong with the 16″ flow wise, just that its best to get as wide as possible for optimal skim.

  3. Rated 5 out of 5

    reefersmexico (verified owner)

    By far, the best overflow I’ve ever owned, the quality of the product speaks for itself, quiet operation, flawless design, with backups for the die hard reefer, I mean, I will never build another tank without a synergy reef overflow. Keep up the good work Synergy! Thank you very much.

  4. Rated 5 out of 5

    Doug (verified owner)

    Just got my Shadow 16″ installed on my new reef build, it is the cleanest looking overflow I have seen. Instruction from Synergy on drilling the tank and install where spot on and the customer service is some of the best in the business.

  5. Rated 5 out of 5

    William (verified owner)

    Great Overflow! I’ve got two of them on my 400 gallon peninsula tank that I preordered, and love them, well built, easy to clean, nearly silent, perfect. I wouldn’t hesitate to buy them again, and have recommend them to friends.

  6. Rated 5 out of 5

    Brandon (verified owner)

    I preordered this when it first came out and have to say that I couldn’t have been more impressed. The quality craftsmanship and customer service are top notch.

  7. Rated 5 out of 5


    I purchased this from BRS. The quality craftmanship is top notch and very well built. I love it. I used it in my 55g long reef tank. The instruction is to follow. I don’t know about their customer service because I’ve never bothered to call them. If i have another tank, I would buy it again and highly recommended it to friends and family.

  8. Rated 5 out of 5


    This is killer! Just installed one on my buddies tank and it convinced me to get one for my upcoming build. The template is perfect and once dialed in, it’s dead silent.

  9. Rated 5 out of 5


    Very impressed with the design and I can’t wait to install it. Hello vacation

  10. Rated 5 out of 5

    ed (verified owner)

    This overflow is definitely one of the greatest inventions in the aquarium world. Looks, functionality, quietness and ease of installation are just a few.
    Thank you for a great product prices super fair!

  11. Rated 5 out of 5


    I wanted one of these overflows the minute I looked at one. Amazing quality and attention to detail. I needed 11/2 inch plumbing(bean animal) as I was also purchasing a SS 34 so it would be plug and play. The Synergy video’s, template, and hole saw gave me the confidence to drill my first tank, 125 gallon. I even drilled the glass with the fish inside after lowering the water. Everything turned out great. So happy especially as it was plug and play with the Synergy sump. Thanks!

  12. Rated 5 out of 5

    connorellis273 (verified owner)

    I don’t normally leave reviews but I felt I had to for this! I bought two of the 16″ Shadow overflows for my 300 gallon and I have to say these are an amazing product. I bought the tank with a lack of knowledge in the world of sumps. It had only bulkheads drains and I liked that because it didn’t take up a huge amount of space in my tank, but the gurgling was unbearable. Yesterday I installed these with the fish in the tank and it was extreamly easy for a DIY install and now all I can hear is a little trickle in the sump and a hum of the pump. If you’re thinking about buying, just do it you won’t be disappointed! I can’t wait to buy a synergy sump next!

  13. mixer911

    Thank you for the Review! This is awesome that you were able to install these on a running aquarium with livestock in it! You were able to experience all the benefits of our intended design of our overflow systems!

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