I'm currently doing the same in a small 20g long. Just needed a plant quarantine tank and had no room inside so I put it on my porch. All I can say is that I use a filter to help with water circulation and lots of plants to such up the nutrients before algae can take hold. I do have a little algae but it's nothing serious. I use fluorite substrate and don't dose any ferts right now. The fluorite was used in another tank for awhile so it's got a good buildup in it. I'll adjust accordingly but should be alright this way.
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