Calcium, Magnesium, and Alkalinity testing

[coolxborg]

Mods - Please let me know if this belongs in the chemistry forum but feels like a newbie question.

Now that i have some softies in the display tank, I started testing for these parameters (should have probably started testing prior to getting them, but I am where I am).

Last week 7/21. My test results were as follows:

Calcium - 460
Magnesium - 1350
Alkalinity - 10.5

This week:

Calcium - 440
Magnesium - 1200
Alkalinity - 8.9

Both using Salifert test kits. Also salt mix is reef Crystals.

My questions are:
- Is it normal to see this drop? I mean im not complaining since my results are quite optimal (i think). However, the drop just confuses me since i didnt do anything different.

- How often should I be testing at this moment? 1x weekly, 2x, or more?


Tank is 150g, with 30g sump. Current inhabitants are Royal Gramma, Clown Goby, Hand Leather, zoas, and GSP.

 

[theatrus]

It is normal for Ca and Alk to drop as calcifying organisms, including algae, consume it. Was there a water change in between?

Mg usually depletes at a lower rate.

Frequency is up to you. With your organisms, nothing is super reliant on adequate Ca or Mg, so I'd stick to mainly testing Alk to see how it behaves in your system.

 

[Ron Reefman]

coolxborg, if you are concerned about what is going on with your water parameter may I suggest this as a way to figure out that is going on and to make yourself more comfortable:

Do a water change and then dose alk, cal and mag to get them where you want them, maybe even a little bit above where you want them. For the next couple of weeks do no water changes (add top off water everyday and don't dose anything new into the tank other than food and RO/DI top off water.Then test every day (at the same time of day) and see how stable they are. If they are stable, start testing every other day for 3 tests. Still stable? Test every 3rd day...

And when doing the tests, make sure you use clean equipment and do the test the exact same way every time. Doing the test just right is probably less important than doing it the same way each time. At least that way you're consistently making the same error and although your numbers may be slightly inaccurate, they will show the proper trend to your water parameter changes.

The point of this test is to figure out if what is going on in your tank is happening quickly or over time. BTW, unless there is something very wrong in your tank, water parameters shouldn't change much at all day to day or even over 3 or 4 days. What you might start to see is a regular, almost linear, reduction in the alk and cal. Mag will go down as well, but much slower.

Given that you have softies, your drop in these water parameters should be very slow as only lps, sps corals and some skeleton and shell making inverts like fish and snails will use any out of your water. Maybe a tiny bit could go into making coraline algae. But your softies have no skeleton, so they use very little if any of these parameters.

 

[coolxborg]

Thanks for the replies. I made two small water changes (10 gallons each time since I was using DT water for TTM).

Ok. Ill do a WC this coming weekend and test daily to see whats going on. Thanks again!

 

[downbeach]

Is there any coraline algae in the tank? Make sure your SG is consistant. What are you using to test it with?

 

[coolxborg]

Very minimal coraline algae. Some live rock that I bought from LFS has some.

Salinity is at 1.024 and using a refractometer to test it. Salifert for Calcium, Alkalinity, Mg.

 

[Sk8r]

When I start a new tank, I often test everything daily once I start dosing, and keep a log so I can track what this particular tank does.

Softies don't consume calcium and mg beyond what your salt mix supplies, as a rule, so you mostly just dose alkalinity buffer to keep them happy.