I think I would stick to a neutral medium like perlite. I read coffee grounds is high in nitrogen and is acidic. This may alter the levels of nutrients and the pH in your solution in ways that maybe difficult to predict. But this is a great hobby and there's no law that says you can't give it a try.

Hi edurink. I know some growers would not consider grounds hydroponic but I thought this was such a neat & inexpensive idea for a media. Hank is right about the nitrogen & acidity, but I just like experimenting. I have tried coffee grind as a seed starting media. If it is placed in a baggie, it will mold. It seems to crust on top & be too moist on the bottom if placed in a cup. Again, mold can occur. Tomato & apple seeds did germinate, but damp off because more aeration is needed. I am trying to mix it with different substances but I am still experimenting.

*used* coffee grounds are not acidic. They are almost neutral pH.