I'm not an expert by any means; I'm a very lazy plant caretaker and never remember to fertilize my plants. I've said for years that to survive under my care (or lack thereof) plants must thrive on neglect. I'm fortunate to live in a climate where my hoyas can stay outside year round where they love the heat and humidity.
Yellowing leaves can be caused by many things; too little water, too much water or possibly something is going on from the root level, upwards. Hopefully one of the more knowledgeable Hoya growers will be able to offer advice and tips on what to look for as the cause. Also, the type of Hoya and a photo of the plant in question might help to identify the issue.
