Definitely too close, if you plan to use sand. Not so much that it would suck up the sand right off the bottom, but when the fish stirs up the sand. I prefer mine at about 6" above the substrate. While my >60% wc doesn't go below the input, I turn my filters, heaters, lights off during wc. Its easy when everything is on a single power strip. Doing it this way, you tend not to forget to turn the heater back on. I also turn the tanks' light off because I find that it makes it a little less stressful for the fish.
I've been running two of those 304b for over 4yrs now without a hiccup. Not bad for huge, sub $100 canisters
For a 125, I would recommend for you to get another 304b or something equivalent in size. Its always a good idea to run multiple devices in regards to filtration and heating.
I've been running two of those 304b for over 4yrs now without a hiccup. Not bad for huge, sub $100 canisters
