Water changes

[PeterEde]

So I've switched to NSW a while ago
Should I ensure the new water meets Calc/ALK/Salinity before doing the water change?
Now I find I am doing the change then testing and having to replenish lost elements.
Wouldn't it be best for stability to have the new water already at 420Calc, 8.5 ALK before the change?

 

[gbroadbridge]

So I've switched to NSW a while ago
Should I ensure the new water meets Calc/ALK/Salinity before doing the water change?
Now I find I am doing the change then testing and having to replenish lost elements.
Wouldn't it be best for stability to have the new water already at 420Calc, 8.5 ALK before the change?

I try to match them - but having said that, I only change 10% every couple of months so I try to avoid disturbing a finely balanced system.

If I were still doing 10% a week, I wouldn't bother - I'd just adjust the dosing pumps.

 

[Randy Holmes-Farley Verified Community Expert]

So I've switched to NSW a while ago
Should I ensure the new water meets Calc/ALK/Salinity before doing the water change?
Now I find I am doing the change then testing and having to replenish lost elements.
Wouldn't it be best for stability to have the new water already at 420Calc, 8.5 ALK before the change?

If you want to do significant changes with natural seawater and are concerned with alk stability, then you may need to boost alk in that water since it will be well below your tank level of 8.5 dKH. But if the changes are small, 10% or less, then that is not likely an issue except that it will lower the tank alk.

I'd test only the salinity in the natural seawater. Everything else should be known from that.

 

[PeterEde]

If you want to do significant changes with natural seawater and are concerned with alk stability, then you may need to boost alk in that water since it will be well below your tank level of 8.5 dKH. But if the changes are small, 10% or less, then that is not likely an issue except that it will lower the tank alk.

I'd test only the salinity in the natural seawater. Everything else should be known from that.

Problem being my local water is far from reef quality. It's temperate water where no corals grow. Salinity is 37 typically so is accounted for

 

[Randy Holmes-Farley Verified Community Expert]

Problem being my local water is far from reef quality. It's temperate water where no corals grow. Salinity is 37 typically so is accounted for

All major and most minor ions in natural seawater (including alk, calcium, and magnesium) the world over are exactly known from the salinity, unless it is locally impacted by river entrances or other additions of water or elements (such as a hydrothermal vent, an underwater spring, etc.). Trace elements vary by location and by depth and even by time of year, regardless of the salinity.