Here is the profile for the Dojo loach: http://www.badmanstropicalfish.com/profiles/profile103.html
As you can see, they need a sand substrate or very small, smooth gravel because they like to bury themselves. They also don't like much current.
If you vacuum the bottom once a week when you do your water changes, you won't have to push the waste into the intake. It can wreak havoc on your filter. Plants can use some of the nitrates but they only help control nitrates if the tank is extremely heavily planted. That doesn't really work with having goldfish because they need some vegetation in their diet. The best thing to do in this case is to keep up with water changes which will remove those nitrates.
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