03-09-2013, 11:03 AM
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The gravel siphon, hovered and/or swirled just above the surface is your best method of removing mulm...if you need to. However, if you have rooted plants, don't over look that this material makes excellent organic fertilizer for those plants as it feeds the substrate bio-filter.
If there is larger plant waste that may clog the siphon hose, I'll sometimes swirl a fishnet to collect it prior to using the gravel siphon.
Some feel that mulm on the substrate is a sign of insufficient circulation or filter flow but this material that settles is best kept out of the filter. Why? IMHO, because the filter with high velocity water flow and decomposition bacteria very quickly erodes, dissolves and converts this material into dissolved organic compounds (DOCs) that pollute the water column. Excess DOCs encourage an abundance of unwanted heterotrophic bacteria and if not cloudy, water that has a yellow or brown tinge and sometimes a fishy or foul odor. The filter is best reserved for collection of suspension 'floaters' and purifying the water.
If/when left on the substrate, mulm decomposes very slowly and feeds the substrate beneficial biology that in turn feeds any rooted plants OR is very easily siphoned away during weekly water changes.