Hi Badwolf, I'm in the process of raising 6 L-144 longfins, which are a type of bristlenose to breed. I've researched a ton and have a tank just for them. Depending on what kind of fish you have in the tank with them the fry would very easily become a meal for a bigger fish.
I feed my bristlenose blanched squash, zucchini, green beans, cucumber, a quality algae wafer, they also get blood worms and
brine shrimp too. The algae on the tank and scrapes may not be enough for him. Mine eat a ton of food and are growing like weeds.
I personally wouldn't put a bristlenose in anything smaller then 20gallon. A 7 gallon is def to small.