Why do my parameters drop from water change?

DomC · May 11, 2015

So I try to perform 10% water change weekly. I'm using Redsea Blue bucket. I match salinity of tank. New batch mixes at ph8.2, 8.3dkh, mag 1280, and calcium 413. I try to maintain 8.2 dkh, ph 8.1, 440 calcium and mag 1300. So parameters are pretty close; but after I perform a water change my alk with drops to 7.3dkh, calcium to 410 and mag to 1200. What can cause this?

Thanks

Dom

cloak · May 11, 2015

How does everything look? If all is well, try not to get caught up in those numbers. Sometimes "within reason" is good enough. GL.

DomC · May 11, 2015

In the past I tired not to chase it but with every water change parameters kept getting lower. At one point alk dropped to 6.3dkh and calcium 380. I do dose 2 parts via dosing pumps. Most of my sps look good with good PE while others have stn. Nitrate levels are +/- 1ppm, Po4 0.03+/-. Growth seems slow as well.

Randy Holmes-Farley · May 11, 2015

The alkalinity cannot drop from 8.2 dKH to 7.3 dKH with a water change. Even if that 10% water change had 0 dKH (like RO/DI water), the alk would only drop to 7.4 dKH.

Doing a water change with 8.3 dKH water, as you did, will cause no noticeable change in alk.

So that measured drop in alk is a measurement error of some sort, or, if you waited for long enough after the change, by some precipitation of calcium carbonate by corals and other creatures, or abiotically.

Same for the other parameters, except magnesium, which won't noticeably be used or precipitated.

DomC · May 11, 2015

That would be my guess some type of imbalance. I'm just not sure how to correct the issue. I usually wait an hour after doing water change to check parameters.