ATB Medium Size 25 – A review of this powerful skimmer

by | Jul 27, 2020 | Equipment | 0 comments

We have never tested such a powerful skimmer before! We measured over 1,300 l/h of sucked air, which we had never seen before testing this ATB Medium Size, 25 cm in diameter.

First of all we want to remind you that ATB is the acronym for Aquarium Technik Burian, an Austrian company with its headquarters in the Czech Republic. It has been producing accessories for marine aquariums since 2001. We tested the skimmer in a 600 liter aquarium specifically dedicated to hard corals with small polyps, in particular Acropora. The beautiful aquarium is Jonathan’s.

As usual, we tested the ATB Medium Size 25 for several months, so that we could discover every pro and con. We can affirm that, especially with the provided accessories, the skimmer really amazed us. The automatic cleaning is addictive right from the start, and the power of the skimmer is simply incredible.

Speaking of the assembly, this skimmer doesn’t hide its artisanal origin. Beautiful and well built, but it doesn’t shine compared to other skimmers we’ve recently seen (Ultra Reef, Red Sea, Vertex, Nyos for example). The declared sucked air is 1,500 l/h while the treated water 2,500 l/h, for an air/water relationship of 0.6 with the Askoll pump.

Technical characteristics of the ATB Medium Size

 ATB with pump AirstairATB with pump Askoll
Treated water volume2.800 l/h2.500 l/h
Treated air volume1.500 l/h1.500 l/h
Pump consumption38 w38 w
Dimensions390x340x560 mm390x340x560 mm
Water height in sump18-19 cm18-19 cm
Warranty24 months24 months
Price980 euro980 euro


The construction is very well done, there are minor flaws, but nothing that could affect the yield. Even though there’s a little detail… but we will discuss it later, because it has to do with the cleaning accessory and not the skimmer itself.

About the functioning, we have an old style setup that suits the powerful pump that these dimensions require. In fact the pump is external, so there’s more space for the bubbles in the body of the skimmer. The pump pushes the water into the central body where the water and the air mixed together are then pushed through the perforated diffusion plate. The central body is conical. The pump is an Askoll that draws from a few cm above the bottom of the sump.

The body of the skimmer has a diameter of 25 cm and it’s almost 56 cm tall, glass included.

One of the added values of this skimmer is the option to buy an automatic cleaning system, built with a little brush attached to a pivot, which is activated via a timer (not provided) that keeps the neck of the glass perfectly clean. Thanks to this, you only have to empty the glass through the bottom cap and… that’s it, without ever disassembling the glass.

The assembly system of the ATB Medium Size skimmer is very simple and it can be disassembled quickly. This is also thanks to its dimensions and the fact that the pump is external.

Given the dimensions, the glass is pretty heavy, though it sticks perfectly in the base where it has to be placed and pushed in a bit. It is secured further with a red gasket. At the base of the glass is the classic opening, from which protrudes the PVC curve closed by a silicon end and a stopper.

The pump that comes with the ATB medium size 25 is an Airstair, an adjustable pump that can push 2,800 l/h of treated water and 1,500 l/h of treated air. In our tests we also used a second non-adjustable pump by Askoll, which can be purchased separately or ordered from Askoll itself, which pushes up to 2,500 l/h of water. The second pump is quieter and has less vibration. But even if we wanted to use both pumps, we had to work within the dimensions of our sump, so we decided to try the skimmer with only the Askoll, which was the only pump that could fit in the available space.

As it has a monopump configuration, we don’t have to manage the water entering the skimmer and the water/air relationship because they’ve already been decided. The suggested level in sump should be about 20 cm, though it can accomodate heights between 18 and 24 cm, as the builder designed.

The functioning scheme is, simple and linear, especially compared to other skimmers we’ve recently reviewed. Moreover, this ATB has an external pump that allows for a higher volume of water and air in the body of the skimmer than in configurations with an internal pump; that also increases the contact time inside the cylinder. The convenience of the external pump is especially apparent when it’s time for cleaning. Water and air are mixed together and, from below, they directly enter the body of the skimmer. From here they pass through the classic perforated plate.

The only way to change the calibration of the skimmer is to rotate the drain pipe, which adjusts the slider that determines the level of water inside the body.

Set up

The set up is pretty complex, not for the skimmer itself but for the various accessories, which have to be purchased separately. The brush inside the glass has to be assembled, and the float inside the glass has to be connected to an external controller that will then switch off the skimming pump when the level in the glass is dangerously high.


The skimmer needed some days of running-in. The foam completely fills the body, as we expected. The foam is really compact and the bubbles are very small. Visually speaking, foaming and coloration seem very good.

The suggested level in sump is, as always, about 20 cm. At that height, the suction of the air and the pressure of the water are perfectly balanced. Obviously (we want to repeat this for the ones who don’t know) they’re in equilibrium because the skimmer has been built in this way, that’s the reason. So I suggest keeping the level very close to 18-19 cm as the skimmer asks; in our tests the slider was at exactly 20 cm. The foaming also strongly depends on the salinity: the more salinity we have, the better the skimmer will work. We have always kept salinity at 35 per thousand.

After six months of use we can affirm that the skimmer ATB medium size 25 has worked perfectly. Perfect values in aquarium, very little maintenance, and always efficient.

The ATB and its maintenance

Thanks to the brushes inside and to the drain at the bottom, the maintenance is reduced to a minimum. Sure, we would have liked to have the same countersink as the Red Sea RSK 600 (review) does, which would have allowed us to keep control of the level of foaming but, beyond that, the skimmer worked perfectly. We placed it in the sump in February and we kept it going until just a few days ago.

Performance and measurements

The builder declares for this skimmer an amount of water of 2.800/2.500 l/h and 1.500 l/h of air, depending on the pump you use. These numbers are influenced by a lot of different variables, such as the height of the water in the sump, the height of the water column inside the cylinder, and most of all the salinity, which we kept at 35 per thousand. The air/water relationship with those parameters is 0.6.

Unfortunately, given the particular conformation of the skimmer with the drain at the bottom we couldn’t measure the treated water. For the air measurements, we used our classic Sander flowmeter, which measures the air from a minimum of 100 l/h to a maximum of 1200 l/h. These values then have to be increased by 10% in order to accommodate for the shortcomings of the device.

We obtained an amount of treated air of about 1320 l/h (1200 collected+ 10%), with the air completely open. The value was pretty stable. Another thing we noticed is that our value never changed, with either a clean or a dirty skimmer. It’s also pretty close to what was declared by the builder, with a gap of 12%. A really good result, our personal record here on DaniReef.

The skimmer is very quiet; the whole aquarium a bit less. We did three measurements, all one meter away from the aquarium and the sump. We obtained the following results:

Sound pressure at 1 meter with all the utilities on and closed doors: 44.6 dB

Sound pressure at 1 meter with the skimmer switched off and open doors: 46.6 dB

Sound pressure at 1 meters after switching on the skimmer: 47.7 dB

The difference in the sound pressure measured with the skimmer on and off is 1.1 dB, very reasonable.

The sound level meter is our usual VOLTCRAFT 320, digital meter IEC 651 Type II which is very reliable. Given the nature of the noise, all the measurements have been done with the attenuation curve dBA.

Maintenance costs

The pump by Askoll with brush impeller and monopump skimmer by ATB has a declared consumption of about 38 watts, that per year is 332 kwh, and an estimated cost of about 90 euro if the cost per kwh remained stable at 0.27 euro.

As usual, we measured the consumption:

We found it lower than declared, just a bit over 36 watts. The difference, practically, is that you go from 90 euro to 85. Unimportant. What we wanted to underline is the closeness between the declared values and our measurements.


Now let’s hear Jonathan‘s thoughts about his experience with the skimmer. But first here’s a glimpse of its aquarium, so that you can picture the testing ground.

Before you ask – yes, Jonathan‘s tank will figure soon in the aquarium of the month on our pages!

Jonathan tells us the skimmer really is quiet and he has been impressed by the very tiny bubbles at its base. The skimmer wasn’t very sensible with hands in the tank or while feeding the fish. Sometimes the administration was right at the same time of the automatic cleaning, set to 2 minutes for 4 times a day. But during the feeding of the corals the skimming stopped and started again after a short time. Easy and comfortable to work the control drain and it’s the only thing you have to do! There isn’t any control on the incoming air, aspirated by the skimmed.

The only flaw, says Jonathan, is that the cleaning system is badly assembled. The brush comes close to the top edge of the neck, as you can see in the previous picture. That little space close to the top of the internal cylinder remains dirty. It probably has little affect on the performance, but on the other hand it doesn’t cost anything to fix this detail in the construction.

It’s the first time Jonathan has found himself with a skimmer that tarnished heavily during the use. It could be why it has few ventilation holes at the top. Anyway, after few days the internal cylinder becomes completely invisible so practically speaking it’s the same. But the problem persists even excluding the tube for the smell recovery. After three days it begins to defog. The timer for the automatic cleaning unfortunately isn’t included, and the float snaps immediately, but if you let it cycle, the pump switches on again.

First impressions

The skimmer is very slow initially, it took 10 days before it began to foam.
During the second week it almost filled up the glass but Jonathan voluntarily set it to be very wet.

The cost

The skimmer ATB Medium Size 25 cm costs 980 euro. The second pump costs 395 euro, but the skimmer can be ordered with either pump for the same price. The automatic cleaning system, that we recommend, costs 299 euro, while the anti overflow system costs 119 euro.


This skimmer is a real monster. Its values are amazing and, if it isn’t enough, take a look at the general conditions of the aquarium, with a lot of beautiful fish and very colorful Acropora. The construction is good, except for some unexpected flaws, like the brush badly calibrated and the lack of a timer. The opportunity to have the float is very good, so that you don’t have to worry about the overfill of the skimmer dumping into the sump. We think that 980 euro for this skimmer is a high price, but in line with its performance. We have never registered 1320 l/h for the intake air before. The cost of the accessories is also high, but once you try them you can hardly do without.

During use it has been consistent and efficient. Easy to open and clean, but an operation that we only a really few times, and that’s one of the features that we will surely miss in the future.

According to us, it’s good for an aquarium of SPS corals and fish up to 700/800 liters. Obviously, if  you have a less-populated aquarium, with only fish or with soft corals, you can push it to 1500/2000 liters.


  • Very high value of aspirated air
  • Very good automatic cleaning system (for 299 euro)
  • Very useful float in order to avoid overfill (for 119 euro)
  • Very silent skimmer


  • Cleaning system should be calibrated better
  • There’s isn’t a timer for the cleaning system
  • High cost, even with the accessories

The ATB skimmers of this review come from Aquariatech, the Italian distributor of the brand.

[Translated by Agnese Poggi]

  • danireef

    Danilo Ronchi, aka DaniReef lives in Italy where he is hydraulic engineer, but starting from his love for reef aquarium and photography, he began to write about marine aquariums from 2006 and now he's published his first book "Marine Aquarium". From 2007 Danilo writes on his blog where publishes articles, pictures, product reviews, aquariums coverage, reportage and history of his tank. Now he's happy to be part of


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