All of my tanks, whether they have HOBs, canisters, or W/Ds also have 1, 2, or 3 40 gal sponge filters running off my main hatchery blower. The blower has 2 backups in case of failure. Each blower will run over 100 tanks with sponge filters and air stones. In fact, the airstones are quick clean capable so, I haven't needed to replace an airstone in 6 years. Several of the larger tanks also have powerhead pumps with venturis. If a filter dies, I have spare FX5s, XP3s, and 500GPM to 5000GPM submersible and external pumps waiting in the wings. I recently lost a large pump and replaced it with a spare. Before the new impeller arrived to repair the original pump, I lost the impeller to the backup. Now, I have spare impellers for most of my mag-drive pumps. I'll soon have backups for all of them.