WCs

The answer depends wildly on what and how much you're adding to the tank (chem- and fert-wise), as well as if it's planted.

you don't have much load for 50 gallons, but that's a tiny filter for that size tank....

also what kevmo said..

I judge my weekly water changes on the nitrate level. I don't change much water in my 37g so I can maintain about 20ppm for the plants while I change like 80% in my 20g. It is heavily stocked and has artificial plants so the nitrates get to 80ppm by the end of the week. But regardless of the nitrate, substrates need vacuuming on a regular basis; because I'm crazy about the cleanliness of my substrates, I vacuum every week with no ill effects on the cycle.

Btw, your pandas will be much happier if you give them some more friends. You could have 10 in there without a problem.

-Lisa

I have a few stems of bolbitus, 2 huge softball sized HM, a softball size of singapore moss, a golf ball of peacock moss, a softball size of najas and hornwort, and 1/3 of the top of the tank is covered in dwarf water lettuce, red root floaters, and frogbit. So, for the amount of flora compare to fauna, I have significantly more (IMO).
Forgot to add that I also have 2 dual sponge filters sitting at the corners of the tank.
There is significant enough water movement, I don't want my shrimp being tossed around, just a gentle current so I think the 2213 is enough.
As for dosing, I've been really lazy. I dose CSM+B at 4mL every 4 days. When I remember in between those days I dose 3mL of KNO3 and K2SO4. Also 1 mL of epsomsalt. Other than that the tank is non-CO2, no root tablets, and the lights are: dual T-5 28Watts (total) that is 24" long and another 65 watt 24" PC bulb.