Nitrate won't warrant wc, how often should i wc?

[ljones]

I had planned, when I set up the 75 gallon, to do water changes once nitrate hit around 10 ppm. Currently, I replace 4-6 gallons a day removing detritus. It's been nearly 2 weeks and I haven't even hit 5 ppm yet. When do I start worrying about DOCs and missing trace elements? Is a large monthly change sufficient in addition to my daily maintenance?

[Tom]

Your O isn't full size and you have lots of water volume (counting the sump), so no big surprise.
I'd still do a water change weekly, but you could do small ones like 25% until you see the nitrates climb.

[ljones]

Eh. My math shows that my day-to-day maintenance is adding up weekly to anywhere from 29% (super conservative, definitely actually more than this) to 41%. The most likely number is the 34-35% in the middle, so I'm getting well over a third of it changed per week as it stands.

[~RuSh~]

If by your math, you are doing 30-40% changes a week I wouldn't worry about trace elements. It takes a while for TDS to build up when you are talking about evaportion and top offs. If that was your only concern then I'd say yes once a month would be enough to bring TDS levels down to what they normally are. Of course, more often wouldn't hurt.