Skimmer problems - looking for some advice

[SmilingTurtle]

Hi everyone! I could really use some experienced advice that might make my life a little easier.

Here are the basics of my system:

• 80L (21-gallon) AIO
• Skimmer: IOAOI, rated for 30 gallons, hang-on
• I modified the skimmer intake by adding a CO₂ absorber canister to help improve my pH, so the skimmer is currently drawing air through the CO₂ scrubber.
• The painted water-level indicator on the skimmer is at the correct water level.
• In the next chamber I have the return pump, heater, and ATO for replacing evaporated water.

The problem​

Every now and then, my skimmer suddenly goes crazy and starts pumping water out of my aquarium. Obviously, my ATO then kicks in and replaces the missing water, which creates a vicious cycle that continues until the ATO reservoir runs completely empty.

What I find particularly strange is that the problem continues only as long as there is water available in the ATO reservoir. Once the ATO reservoir is completely empty, the skimmer stops doing this and everything goes back to normal. From that point on, the skimmer continues working normally without any further issues.

My first thought was that maybe something is wrong with the skimmer's air intake. But even if the airline were completely blocked, wouldn't the skimmer still physically pull water out of the aquarium? (At least that's how I understand it.)

One more important detail I forgot to mention: my ATO reservoir holds around 4 liters (about 1 gallon), while the skimmer has its own external collection cup with a drain tube, which can hold roughly 1 liter.

So, if I'm unlucky enough for the ATO reservoir to be completely full when this happens, I could potentially end up with a flooded room. Luckily, today there was only about 0.5 liters left in the ATO reservoir when it happened, so thankfully nothing overflowed this time.

So I'm really not sure what could be causing this.
Has anyone experienced something similar with an AIO skimmer? Any pro tips on what I should check or how you solved it?

Thanks in advance!

 

[tzabor10]

Check the impeller? This can clog up and create an inconsistent skim. Also the co2 scrubbing media or air line can get restricted.

 

[get-salty]

Lets eliminate the ATO, With out it ofc water level is consistent - so skimmer is happy w/ the water level so skimmer does what skimmer does.

Now, lets add the ATO into the situation, ATO adds water into the tank when water in your display drops below the ATO sensor. When this happens, water rushes into your display and into your drain - which i am sure you're using some sort of filter (sock or floss). Depends on how dirty the filter floss/sock is, this restricts water flow into it causing inconsistent water level for the skimmer.

Long story short, it can be frustrating and difficult to keep a small AIO running smoothly with many add-ons. With that said, I really feel like with a 20gal AIO, a weekly or bi-weekly WC is more than efficient to maintain the water quality. I truly believe that a skimmer on anything smaller than a 20gal is not needed due to the amount of live stocks you can keep in it.