Originally Posted by sk8rvendz
I just recently learned about sponges and the ill effects of carbon in a planted tank. I had a sponge cycled, but needed to use it to cycle another tank. Once the newest one appears to be ready, I'll remove the carbon. I'm a little nervous about having so little filtration in a tank, but from what I've seen on this forum, the sponge should be all I need.
Any advise on the change over? Or is this a just do it moment?
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I will assume we are talking about the 60g tank outlined in your initial post in this thread.
The sponge filter will be sufficient. I would remove the HOB filter. [As an aside, carbon wears out, how fast depends upon how much "stuff" it is adsorbing, but at some pint it can hold no more so it becomes ineffective as carbon and needs replacing. But in a planted tank as you've learned, carbon and any form of chemical filtration is unnecessary and probably detrimental to plant growth.]
I would increase the volume of your weekly water changes to 40% of the tank. You don't have anywhere near sufficient plant growth to handle that fish load, and even if you did the benefit of a water change cannot be understated. And this has no direct relation to the filter, just in case you're wondering if leaving more filters will offset this; it won't.
Filters move water around. Mechanical filtration (through media, pads, etc) removes suspended particulate matter from the water as it passes through the filter. Biological filtration handles the nitrogen cycle, nothing more, but in a planted tank this is not really an issue unless the tank is overstocked. Plants consume more ammonium (from ammonia) than nitrosomonas bacteria by being generally quicker at grabbing the ammonia. Nitrifying bacteria in a planted tank are fewer in number than would be the case in the same tank without plants, and this should be encouraged by limiting the biological filtration capability. Which is why the sponge filter is sufficient.
However, substances in the water cannot be removed except by plants [but only when plant growth is heavy with very minimal fish load] and water changes. i realize some low-tech planted tank authors recommend few or no water changes, but that is not my thinking and with 20 years of doing major water changes in heavily-planted tanks, I have seen no detrimental plant growth resulting from the water changes, and I know the fish benefit.