I've been keeping bimacs for over two years (I'm currently keeping my second) and I can tell you how I do it.
Why the preocupation with live food? I only give my bimacs live food as a treat, when I'm at the beach anyway and I find it easy and convenient to grab a little shore crab or muscle. I feed mostly pieces of thawed frozen scallop or sometimes shrimp (thawed in a cup of luke warm tap water). Be sure to buy raw, not cooked, frozen food. He only gets live food a few times per year. I offer the food at the end of a wooden skewer. I use the skewer to play tug-of-war with the octo for a little while, always letting him win, so that he gets to feel like he had to "subdue" his food. Live food is more fun for the octopus, but certainly not nutritionally necessary, and in a little 30 gallon tank, the mess left after eating a live crab is a danger to your water quality.
I think you should forget about live food, and worry about more life threatening things, like water that's too warm, a tank that's too small, low oxygen levels in the water, and water quality.
Average Water temp in the wild where your bimac lives ranges between 58 in January and 68 in August. I've read that Bimacs seem to "do fine" at room temp (72) but I strongly suspect that at such sustained high temps, like reptiles, they live "faster" (eat more) and die younger (especially in LA
). If you don't have a chiller, but you do have pumps and lights, your water temp could easily be 80, which I suspect will be a bummer for a bimac. I've found used, sufficiently large, chillers on Craigslist (1/6th to 1/4 horse power) for $150 to $300, so if you don't already have one, please keep your eyes peeled and try to get one.
A 30 gallon cube tank is about 19"x19"x19", and my adult bimac's arms are about 20" long, so I hope you have a really small bimac, and that you plan on getting a tank that is at least 50 gallons (60 if it's a cube) before long. If you're using live rock in the tank for filtration then the octo will have even less space. The low water volume is a problem for water quality because there's less water to dilute a big octo-poo or an inking incident. A big sump, that contains most of the live rock, would be a great idea, and easy to do.
Octos need high oxygen saturation in the water, and if you have a lid on your tank, to prevent escapes, then you need a sump, skimmer, air stone, or some other way to let the water do lots of gas exchange. 75 degree water holds a lot less oxygen than 60 degree water (like in the local ocean), so not having a chiller makes things harder for oxygen transport too.
Were the magnets you siliconed in around the top of your tank on the wet side? Were they factory sealed in epoxy, or might they rust or corrode? Don't trust your silicone to keep rust from getting into the water.