04-04-2010, 09:27 AM
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I would personally replace it with a skimmer. Let me give a few reasons why.
First, the mechanical filtration can be problematic long term. As organic waste bonds to any surface, it begins to break down. This biological breakdown introduces both phosphate and nitrate into the system. Additionally, it removes a carbonate ion during this process, lowering alkalinity and causing long term calcium and pH fluctuations.
You could continue to use the hang on, but simply throw a bag of carbon inside it. This passive filtration allows carbon to absorb organics that tint the water color, allowing light to penetrate more efficiently. By not forcing water through the carbon, the negative effects are drastically reduced. I personally do this by throwing a bag of carbon inside my sump.
You will also not a decline in water flow if you remove the hang on, so you could even consider running it empty. I always found the top/down water flow from a hang on to benefit reef systems, but the added salt creep is a frustration so I don't always discuss this.
Replacing it with a protein skimmer would be the best option, because the skimmer will REMOVE the same organics that are being trapped by the hang on. Removing the organics (acids) allows for more stability in the carbonate buffer system that controls alkalinity and calcium levels, and as such the pH.