So-called surface skimmers have been on the aquarium market for a long time. Versions made of stainless steel or glass are now fairly new. With the latter, it sometimes happens that the skimmer does not work quite right. Here we give helpful tips and tricks on this.

Design of the glass skimmer

Largely regardless of the manufacturer (Aqua Rebell or Aquasabi), a Skimmer Glass usually consists of three different parts. The centerpiece is the curved glass tube, which functionally serves as the filter inflow, in the sense of a Lily Pipe. The glass tube is able to draw in water at two points: at the upper and at the lower end. At the latter, there are slots for drawing in the aquarium water. A special, triangular plug that can be rotated can be installed there. Depending on the rotation, the plug can cover the intake slots completely, partially or not at all from the inside.

The so-called float is inserted at the upper end of the glass tube. It is not made of glass (that would be too heavy) but is usually made of high-quality acrylic. In principle, it is a freely moving tube extension with a float body and a special intake device made up of several prongs. Thanks to this special design, the float is able to draw in the water just below the surface. If you now install the complete glass skimmer in the aquarium and connect it to the external filter's inlet, the skimmer is ready for use. The float moves completely freely on the water surface and can thus adapt to the constantly changing water level of the aquarium (due to evaporation, for example). This well-functioning float is necessary for the correct operation of the entire surface skimmer. Unfortunately, certain problems sometimes occur here, which we will look at in more detail later.

Operating and adjusting the Skimmer Glass

Now that we understand the design of the skimmer, consisting of the glass body, float and adjustment piston, it is easier to talk about the adjustment options. Connected to the external filter, the glass skimmer is now able to draw in water both through the intake slots in the lower part and through the float at the water surface. With the adjustment piston at the lower end, the aquarist can now close the slots more or less. As a result, the proportions of how much water is drawn in from above and from below can be shifted in a targeted way. In the extreme case, this means:

• Intake slots completely open at the bottom - the water is drawn in mainly from below.
• Slots completely closed - the water is drawn in mainly from above.

Between these two positions, many small intermediate settings are of course possible.

Problems with the glass skimmer

A problem that sometimes occurs with these glass skimmers can be that the float does not work correctly. Either it is not drawn under at all or it is only drawn completely under water. Or the float keeps bobbing up and down.

Important: A pump capacity of at least 650 liters per hour is required for the glass skimmer to work correctly!

With insufficient pump capacity, the float is not drawn in properly or not at all, even if the intake slots at the bottom are completely closed. For the most typical cases, we have created the following FAQ.

The float does not draw in any water at the top.

• No biofilm has developed on the surfaces of the float yet. If the skimmer has only just been installed, it helps to simply wait a few days.
• The float is dirty or clogged. Cleaning fixes this problem.
• The setting of the piston is wrong. The remedy here is to close the intake slots further.
• As already mentioned above, insufficient pump capacity can be the cause here. Please note that it gets worse as the filter runs for longer. If this is the case, the filter materials and the filter hoses should be cleaned to get a better flow rate again.
• If this problem occurs even under optimal conditions, an air cushion under the float that is too thick can be the cause. This makes the resistance too great for the float to be pulled slightly under water. However, this air bubble can be reduced by gently waving your hand or, in a very targeted way, by drawing it off with a small air tube connected to a syringe.

The float is only drawn completely under water.

• The float is dirty or clogged. Cleaning fixes this problem.
• The setting of the piston is wrong. The remedy here is to turn the piston so that the intake slots are opened further.
• The filter's pump capacity is too strong. It helps to throttle the flow a little.
• The air cushion under the float is too small. To refill it, pull the float completely out of the water once and dip it back in.

The float bobs back and forth

This happens when, on the one hand, the resistance of the float (due to the air bubble) is just as strong as the suction of the filter. Here too, the usual measures help:

• No biofilm has developed on the surfaces of the float yet. If the skimmer has only just been installed, it helps to simply wait a few days.
• Raise the water level.
• The float is dirty or clogged. Cleaning fixes this problem.
• The air cushion under the float is only slightly too large. By waving by hand or with the help of the syringe and tube, you can reduce the air bubble a little in a targeted way.