Mulm Farm

So I think I've concluded that my Eheim Classic 2213 is not nearly big enough to filter my 29 gallon aquarium. Even though Eheim states it can be used on up to a 60 gallon tank, I seriously doubt a normally stocked, planted tank would be filtered effectively by the filter. Don't get me wrong, the filter is amazing in every other aspect. It only uses 5W, it's easy to clean, it only needs to be cleaned every 3 months or so, and it just works well. But my tank has 15 fish in it (a little overstocked by the 1 inch of fish to 1 gallon rule) and the Eheim just cannot keep up. Some are very messy fish, like my 3 Bosemani Rainbows and 2 Gouramis, and since I've had it on my tank I've noticed a layer of mulm and debris slowly building up. It's gotten to the point where it has started to actually choke out my Dwarf Hairgrass and Blyxa japonica. The filter claims it has a flow of 116gph, or roughly 100gph with media. This is just not strong enough to keep the debris and mulm from settling on everything, making a mess. Even if I added a power head, I doubt the filter would be able to suck up enough stuff to stop it from being a mulm farm. Either way, it looks like I'm going to have to come up with a solution, which probably means buying a new, more powerful filter.