Water Change question

[PufferMe!]

I have a FW tank, and routinely do 50% WC weekly. But, given that my marine tank is large and salt gets expensive, I'd like to know more about WC's needed with SW.

My tank is 70 gallons. I have live rock and dead rock. I'll have a skimmer on it in days (waiting on a pump). I have 2 powerheads running, a emperor 400 and a fluval canister 405. Due to evaporation, I add about 5 gallons each week to top off tank, with mostly freshwater to keep salinity at 1.022. The tank has been running, cycled about a month. I was initially getting nitrate readings of about 10ppm. Suddenly, it went to 0 and has stayed that way. My water parameters are as follows for the last 3 weeks: Ammonia 0, nitrites 0 and nitrates 0. Assuming my water stays like this, wouldn't I still have to at some point do a WC and how much? I took out 5 gallons a couple days ago, just to vacumm the gravel a bit, but wonder how often others do WC with a marine tank?

Thanks

Gwen

[Pufferpunk]

I do ~30% every month.

[Terrance]

its hard to tell with a skimmer. maybe 50% every 2-3 weeks? it depends on total water volume and stocking.

[PufferMe!]

I like Pufferpunks response best The reason I ask is because I wonder if water changes are for more than just because of nitrates, but I don't know for sure with marine?? I'll do a once a month change, even if I have 0 nitrates. Of course, more often if I have nitrates at 20ppm

Thanks

[RTR]

If you also track the pH and the carbonate/bicarbonate hardness (KH) you can get an idea of the water stability. If you lose detectable KH, you need water changes. But all presumes that your skimmer is in place and operating well.

[kv2wr1]

I do a 20-25% weekly water change on the display and do a 60% weekly on QT if fish are in there since the filtration isn't as good as the display tank. If the display is fallow, then I would do less of a water change.

[Pufferpunk]

Why do a WC on a fallow tank?

[RTR]

Clarification is needed: Define "fallow". It usually means or implies "idle" and unoccupied. Bur a FOWLR +skimmer +macroalgae refugium has the second highest BOD (Biological Oxygen Demand) in captive systems even without fish in it (Reefs are the highest), so if it is w/o fish, it still need feeding and water partials to keep all the LR, infusorians, micro- and macro- inverts, bacteria, etc. alive and functional even if operating w/o the fish load. I would keep feeding it and doing partials just as with any cycled tank, just at lower levels of food and partials.

It the tank is truly idle - no LR, no pods, no macro- or micro-life form (i.e., not cycled),it needs no food, then I would not do much if anything with it either. If is still biologically alive, it needs care, feeding , and partials. That care is scaled to food input level however.

HTH