How to stop a skimmer from overflowing

Protein skimmers fall into the category of ‘absolute necessity’ if you own a saltwater aquarium. They work tirelessly to remove unwanted dissolved organics and detritus from the water passing through your sump every minute of every day. When dialled in correctly, a skimmer will just work, bubbling away in the background. Your only requirement is to regularly empty and clean the collection cup. However, every reefer knows that a skimmer has a mind of its own. Sooner or later it will go nuts, leaving you scratching your head and asking how to stop a skimmer from overflowing.

how to stop a skimmer from overflowing

Protein skimmer overflowing in a new setup

The most common cause of an overflowing protein skimmer is the combination of a new skimmer in a new saltwater system. The reason this happens is due, in part, to the viscosity of newly mixed water. Viscosity is the measure of a fluids resistance to flow. In terms of a saltwater aquarium, when a new tank is filled with new water, that water contains almost nothing in it to create resistance, or make it thicker or stickier. As the tank matures, and dissolved organics, detritus and waste increase, the viscosity or thickness of the water increases. When the water is thick enough, or viscous enough, the skimmer will start to kick in.

How to stop a skimmer overflowing in a new tank?

Unfortunately, this is a waiting game that can take up to 6 weeks. There are however, are a few things you can do to mitigate the over-skimming. In a new tank, it is unwise to turn a skimmer off, especially if you have already added fish. 

1. Raising the skimmer

By placing the protein skimmer on a raised platform, you are increasing the height that the bubbles have to climb. This could limit the amount of water accumulating in the collection cup. The IceCap adjustable skimmer stand is made for just that purpose. In fact, the stand can also be used in sumps where the aquarist may be asking, ‘Will skimmer work if water level is high?’ The stand can be adjusted to suit your purposes.

2. Drain the overflow with a collection cup hose

If your skimmer is equipped with a collection cup outlet hose such as the Red Sea Reefer Skimmer, keep the valve open and position the end of the hose in the return compartment of your sump. Sometimes however, the amount of overflowing water can overwhelm the ability of the hose to drain it.

3. Remove the collection cup lid to allow the overflow

If the water flow is overwhelming the collection cup, it may be worth removing the lid to allow the water to overflow back into the sump. I have had to do this once or twice in the past, but found that the inside cabinet was getting drenched from the accumulation of popping bubbles. To prevent the mess, I placed a plastic shopping bag over the cup to contain the overflowing bubbles.

4. Remove the whole cup for the skimmer to overflow

This is an option, but in my experience, not ideal. Without the cup attached, there appears to be no funnelling action to slow the water down, even slightly. The water cascades at speed over the body of the skimmer. This makes it difficult to place a plastic bag over the body as it quickly becomes dislodged. In addition, you will have no indication of when the skimmer kicks in because the collection cup is not there as a visual guide.

Why is my skimmer suddenly overflowing in an established tank?

A few of the known reasons for a skimmer going mental are detailed below, and as all of them are a purposeful addition, you can be proactive in ensuring you minimise the disruptiveness it can cause. But what happens if it is unexpected with no apparent warning? Read below.

1. Red Cyano Treatments

Chemicals such as Chemiclean have an immediate affect on the viscosity of the water in your tank. The moment you put it in your aquarium, you can expect your skimmer to go nuts. During the treatment, however, it is important to keep your skimmer running as red slime treatments diminish the oxygen in your tank. Use the step provided above to either divert the flow through a hose outlet, or rove the collection cup lid and place a plastic bag over the skimmer.

2. Supplimental Foods

Adding food supplements can sometimes have an adverse affect on your skimmer, causing it to briefly overflow. Supplements such as Selcon and Prodibio Reef Booster are known cause. It may be a good idea to turn your skimmer off for 30 mins after feeding.

American Marine Selcon 60 mL
  • Excellent for soaking freeze-dried foods.
  • A must for filter-feeding invertebrates.
  • Boosts the nutritional value of live brine shrimp.

3. Clean & dry filter socks

If you have been replacing your dirty filter socks every few days with clean ones, without socking them first, you will already be aware that they will make your protein skimmer go mad. The simple reason is that for the first 30 minutes or so, the water running through them has changed viscosity again. To counter this, prepare your socks by placing them in a bucket of clean saltwater and soaking them, before adding them to your tank.

How to stop a skimmer from overflowing in an established tank?

Any reefer will tell you that they have experienced their skimmer going nuts for no apparent reason. The skimmer could be properly dialled in, and then suddenly you have an unruly bubbling monster spurting your carefully collected skimmate straight back into the system! With the skimmate now in the aquarium, the skimmer will continue to overflow until you do something about it. But what do you do??

Red Sea Reefer Skimmer

Gadget fixes to prevent a skimmer from overflowing

Unfortunately there is not a whole lot of choice, but if you are based in the UK or Europe look out for the DD Skimmer Guardian, sorry US, you don’t have it yet. This works by plugging the skimmer into the Guardian, with a sensor located in the collection cup. When to cup fills to the level of the sensor, the Guardian turns the skimmer off.

If you have a Red Sea Reefer skimmer, or intend to get one, you are in luck. Existing Red Sea customers (at the time of writing this article) will soon have an upgrade option to a DC pump and water sensor probe. If water moves up the skimmer body and comes into contact with the sensor, it stops the skimmer immediately.

See the video here.

Temporary Fixes for an overflowing skimmer

The fixes below will tide you over until you have the time to remedy the situation when you have more time on your hands.

1. DC operated protein skimmer

If you have a DC operated protein skimmer pump, you have the option to turn it down to minimise the overflow at the controller. You might be lucky enough for this action to return the skimmer to collecting, but it may be a very wet skimmate that will need to be emptied repeatedly until things return to normal.

2. Reducing skimmer water height

Dial down the water height in the skimmer body. This is normally achieved by turning a knob on the upright tube beside a conventional skimmer. Of course, this could still create a huge amount of bubbles that will quickly engulf the skimmer cup, which is why the plastic bag idea helps to contain the mess.

3. Use the collection cup drain hose

If your skimmer collection cup is equipped with an drain hose, open the valve and place it in the return compartment. This will help to continually empty the collection cup.  

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The permanent fix to stop a skimmer from overflowing

Your aim is to remove the cause of the overflowing water. Ironically, this can be achieved through the skimmer itself. The skimmer is actively trying to remove the offending waste, but it is unable to cope with the quantity. If you had an industrial skimmer, you wouldn’t be searching for a solution. If you have a collection cup hose, place the end in an empty bucket and let the water drain into the bucket.

1. Collect and remove the waste

Allow yourself at least an hour to get your skimmer running smoothly again. Your goal is to remove ALL the waste that your skimmer produces and remove it from the system. This is easily done with a collection cup drain off hose directed into a bucket. If you do not have a drain off, you will need to wait for the collection cup to fill up, turn off the skimmer, empty and return the collection cup.

2. Replacing water that you remove

Take a note of the volume of waste water being removed, and replace it immediately with freshly mixed salt water to ensure you are not upsetting the aquariums workings. If you leave it for too long, the return compartment will drop and send bubbles into your display.

3. Patiently bear with your skimmer

At first you may think that you will end up replacing the entire water volume of your aquarium. Bare with the skimmer, and you will begin to notice as you remove and replace water that the water being force up the skimmer body is beginning to subside. Slowly but surely you will get to a point where the operation of your skimmer is returning to normal. Pour yourself a coffee and hang out with your cat. This technique is guaranteed to stop a skimmer from overflowing.

stop a skimmer from overflowing permanently

My experience stopping a skimmer from overflowing

I have had to carry this procedure out a few times and I am always done within an hour. My system volume is 148 gallons, and I have found that I normally have to drain off and replace approximately 2 to 3 gallons of water. In my experience, if I have a considerable amount of skimmate in the collection cup, and for some reason the skimmer goes wild, it is the skimmate that needs to be recollected before the skimmer will calm back down. If the collection cup is clean, it is simply a matter of emptying out the cup and service resumes as normal.

Hi, my name is Craig.
I am the owner of The Salty Side.
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How To Stop a Skimmer From Overflowing