My air-stone likes to float. Air being pumped into air does nothing to aerate my nutrient solution, so I had to devise a way to secure the stone to the bottom of my reservoir. I had a suction cup attached to metal ring, from an iPhone screen replacement I just did, so I ran the air supply hose through ring and stuck the suction cup to the bottom of the reservoir. Perfect, it didn’t float up to the surface anymore.
I ran the pumps for a few minutes while I figured out my preferred placement for everything, then I shut it down and left it while my seeds germinated in the closet. When I came back to clean all the components of the system, and put the water/nutrient solution I noticed that the cheap metal ring was already rusting and causing discoloration in the water. I pulled it out of the water, drained and cleaned the reservoir, and thought about what I could do to keep the air-stone down, without introducing rust into the system which would potentially disrupt the balance of the nutrient solution.
The answer, as it often is, was zip ties! I love zip ties. I put a zip tie through the suction cup and around the hose as it went into the back of the air stone. I added another zip tie around the air supply line just behind the other to prevent the first from sliding down the barb of the air-stone and falling off.