how often for waterchanges?

[anark]

with planted tanks...do you still do water changes every week? or should you let the food and waste sorta accumulate and let the plants take care of it?

i've been vacuuming and doing 10-20% water changes everyweek and my plants aren't doing that well.

33g
40watts
lightly planted with hygrophila polysperma, limnophila sessiliflora and ludwigia repens.
flourish tab at the roots and occasion dosage of 'plant gro'

sorry...no iron testing =T

Allan!

[Blinky]

I do a 50% weekly water change - it's a good idea to do it weekly so that less-used nutrients won't build up, it balances things out. IME it seems to keep everyone (fish and plants both) quite happy.
I wouldn't vacuum the substrate too much; maybe run the gravel vac over the surface, but don't disturb the substrate much - plants' roots are delicate and they don't like too much disturbance, as well as the fact that if you're vigorously vaccuming you could cut roots by mistake.
This may not be the reason your plants aren't doing well, though. With 40W on a 33g, that's a bit low. Also, testing is (IMHO) really important. It's the only way to tell if your plants are getting the nutrients they need, as well as making sure that nitrogen/phosphorous levels aren't building up too high for the fishes' comfort.

[geoffgarcia]

if you test your water quality you should be able to tell when the levels start getting outta whack, thats when ya want to change your water.

If you can go more than a few weeks you might want to consider dosing with trace elements for both the fish and plants.

[beviking]

What is your fish load? How often do you feed? I agree you should have some test kits (at least nitrate). My spare plants/fish tank is a 30 (was a 33gal) and I had 40 watts over it. Plain gravel with mulm under it, 8 or so platies/swordtails, an otto. I fed it every day, didn't test much, changed 30% every other week (never gravel vaccumed either) and it was/is clean. There isn't much growth on the plants, but they're healthy.
Your water change regime is fine, but maybe take it easy on the gravel vac (as per Blinky).

[anonapersona]

By vacuuming, do you mean going into the gravel to vac, or do you just wave the suction around to pick up loose fluffy mulm?

You may just have to find the point of balance for your lower light level. While the 50% weekly water change is important for the higher light, well fertilized tank, you really are not in that catagory. You ought to be fine with lower changes.

Recent research shows that at lower light levels, added CO2 can help plants use available light more efficiently. At low levels of CO2, added light can help plants use CO2 more efficiently. If you are not happy with plant growth, those are the two main options to consider.