Water Changes

I have a 29 gallon bio cube.  By the time you subtract for live rock and sand it is 25 gallons of water.

Id still do water changes too, for me I just do a 15% once a month in my mind it helps bring in some of the elements from newly mixed saltwater

Not to mention that this a way to export nutrients also

disneymania wrote: Brad why 12% why not 10% ?

Evaporation and water changes are two VERY different things. Saltwater does not evaporate from your tank, only fresh water evaporates from your tank and should be replaced with pure, clean, preferably RO filtered water.

Water changes do export some nutrients, but keep in mind that it also introduces other things to your tank. Just one example, silicates are added to salt mixes to keep it from clumping. Silicates are a food source for nuisance algae. Also a 10% water change will only reduce nutrient levels in the water by 10%. Effective biological filtration through LR, LS and macroalgae is, in my opinion, much more effective.

we tend to do about 10% every 2 weeks then 15% the other 2 weeks

If you look back at the history of this hobby, water changes were a definite must on the maintenance list.
That was before we knew how to keep things in line with adequate biofiltration and inexpensive supplements. Some atypical tanks are so overstocked with fish and overgrown with coral that the rule book gets thrown out the window.

I'd say that 75% of ~1000 reef tanks I've seen can do just fine with a 10% monthly water change. The key is setting them up with efficient biofiltration and knowing what and when to supplement. I end up changing 10% every 1-2 months.

This is a good question and a much debated topic.  I personally do water changes every...time I feel like it.  That usually ends up meaning about 15-20% every 3 or 4 months.  It's probably been 3 months since I've done one, but I'll likely do one next week.  At any rate that would seem to mean I don't find them very important.  However, I actually do think they are important.  Why?  Because my tank looks awesome after a water change.

Almost every "Expert" in the hobby will tell you how important water changes are.  Anthony Calfo suggested weekly 100% water changes last time he spoke here.  (Of course that was for a nano tank, but still...) 

Nearly every single public aquarium that has the ability does 100% water changes anywhere between daily to monthly.  Many of them do this with natural seawater pumped into the aquarium directly from the ocean, but it still counts as a water change.  I'd bet most of their professional aquarists would tell us how important these large water changes are even though they also have massive filtration systems.

On the other hand I have seen some beautiful tanks that have rarely if ever had a water change.  One example I can think of is the Winterbottoms tank.  Shawn claims to have never done a water change and his tank is fantastic and it has been for years.

Let the debate go on...

I always top off with RO water, Not Salt Water.