Simple green solution. Make up a strong batch, pour it in and let it sit overnight or for a day or so then flush A LOT.
Use an air conditioning evaporator coil cleaner and run or pump it through the chiller as you would your normal solutions. It will break down any bacteria and molds And get rid of all smells and all the indoor cleaners are safe to breath and safe for surrounding environment. Then flush it with clean water. I'm an air con engineer in the uk and this is what we do on smaller chillers. I'm sure you will be able to get it from one of the big stores. If you can't get any coil cleaner use a hard surface cleaner or antibacterial cleaner.
I would go as high as 50/50, but flush it a lot before putting it back into service. Also, if you have used the chiller for a long time, you might want to be aware that the nutrients can eat the crap out of the thermocouple causing the chiller to run colder then the setting.