Tell him (your friend right...) to go slower.
We have a ceramic pot, probably 40 gallons, with no filtration and top it off with hose water. Mosquito fish and some water hyacinths and other plants grow in it no problem. The key is to let all the beneficial bacteria from introduced plants start to grow. The "dirtier" (it will start looking pretty nasty) the thing gets with microscopic organisms the healthier it gets.
We have a couple biological ponds at school that have been run the same way for 8 years. Just try not to fall in after it builds up the organisms; I've learned the hard way a couple times...
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