How do I keep my hummingbird feeder from molding ??

Wash and refresh regular mild soap hot water. Rainse well before refilling.

I don't know where you live, but if you are in a hot climate, only fill your feeders 1/2 full and clean and refill them every few days to prevent mold from getting a foothold.

I make my syrup on the stove,making sure it boils for a while, then bottle it up in a very clean bottle and keep it in the frig. I let a cupful (the amount my feeder holds) come to room temp, then empty, clean and wash out the feeder with hot soapy water before filling with fresh syrup. A tiny brush, like a mascara wand is perfect for scrubbing out the tiny feeding holes!

What works for me is filling the sink and add some detergent and a few tablespoons clorox, the feeder will soak (sometimes I'll do it before going to bed and rinse it in the morning.) It prevents mold from forming and the smell goes away in no time. They don't seem to mind.

You have to change the sugar water every 4 to 5 days and rinse thoroughly with hot water ~ we have them at our home ~ a lot of work but worth it!!!

I have been feeding humming birds for years. You have to keep the feeders clean. In the hot of the summer sometimes I clean them twice a week. The cloudy water is not good for them. I make my own food 1 part sugar, 4 parts water, bring to boil for one minute, let cool. I keep the extra in the fridge and use later when I clean out the feeders. I buy feeders that have a perch for them to sit while drinking and comes apart for easy cleaning. I found some really great feeders that I twist apart clean the inside out and then twist it together. The fancy feeders are sometimes not the best for keeping clean which is very important in feeding hummers. I also get a lot of Orioles at the hummingbird feeders.