Why isn't my CA and ALK consumption balanced? [Archive]

Phludd

08/25/2015, 07:46 AM

First off here are some details on my water/tank:

475 CA
10.5 dKh
1380-1400 Mg
1.024 Sg
1-2 NO3
<1 PO4

It is a 29gal BioCube fully stocked with SPS and a few LPS. I do 25% water changes every 2 weeks.
For the last 9 months I have been using Reef Foundations A/B/C (all separate liquids) administered by a doser.
For a while the CA and Alk consumption was pretty balanced.
For the last month or 2, I have been using .6 dKh and only like 4ppm of CA daily. This equates to dosing 6mL of Alk per day and only 2mL of CA. Everything seems fine, growth is good. I just can't for the life of me figure out why there is such a variance between my Ca and Alk now.

Any ideas?
Do I need to be concerned?

downbeach

08/25/2015, 07:48 AM

First off here are some details on my water/tank:

475 CA
10.5 dKh
1380-1400 Mg
1.024 Sg
1-2 NO3
<1 PO4

It is a 29gal BioCube fully stocked with SPS and a few LPS. I do 25% water changes every 2 weeks.
For the last 9 months I have been using Reef Foundations A/B/C (all separate liquids) administered by a doser.
For a while the CA and Alk consumption was pretty balanced.
For the last month or 2, I have been using .6 dKh and only like 4ppm of CA daily. This equates to dosing 6mL of Alk per day and only 2mL of CA. Everything seems fine, growth is good. I just can't for the life of me figure out why there is such a variance between my Ca and Alk now.

Any ideas?
Do I need to be concerned?

Have you changed your salt mix, or WC amount or frequency?

Phludd

08/25/2015, 07:53 AM

Nope, I always use the purple label Instant Ocean. I have been on the same bucket for 6 months. I always test the NSW before adding it to my tank and then test my tank 6 hrs or so after the water change, just to see if the levels need adjusting. I have been doing bi-weekly changes for about 4 months now.

The only thing that has changed over the last couple of months is some new coral additions. But it is my understanding that regardless of bioload or type of coral, that Ca and Alk should always be consumed in roughly a balanced ratio.

downbeach

08/25/2015, 08:25 AM

Your uptake will increase, not only with the addition of more stoney type corals, but also the growth of coraline algae. Keep in mind that our hobby grade test kits have a rather large margin or error, so it will be hard to accuratly measure down to the numbers your are quoting. The uptake of Ca and Alk, by “stony” type coral, coralline algae, etc. in a reef system is 20 ppm Ca to 50 ppm(2.8dKH) Alk(CaCO3), which is a ratio of 2 pts Ca to 5 pts Alk (2:5), (http://reefkeeping.com/issues/2007-04/rhf/index.php#5) including abiotic precipitation. [I]Equal doses of any two part supplements are designed to provide the same ratio's. One of the things that can skew that is your WC's, sometimes due to differences in the SG, and its ***ociated elements, i.e. Ca, Mg and Alk, your WC schedule, i.e. different frequencies/volumes of water. Also the mix of the salt mix itself, i.e. it has been noted that the elemental grain sizes can settle into thier respective grain sizes during shipping, and give you differing amounts when you make up your water. A good mixing of the salt mix when you first open the container will help to mitigate this possibility. Another thing to consider is the fact that when you keep your elements, Ca and Alk at those elevated levels there is a greater likelyhood of abiotic precipitation, with it collecting on your pumps, heaters, etc.

Here are a couple good articles worth reading:

http://reefkeeping.com/issues/2004-12/rhf/index.htm

http://www.advancedaquarist.com/2002/11/chemistry

Phludd

08/25/2015, 08:53 AM

Good info, thanks downbeach.

I know home test kits can be inaccurate, but even though they may not be precise the tests have been consistent. They do seem to properly reflect the adjustments I make and provide a fairly reliable baseline to test against.

So what I think I heard you say is that it may be beneficial to try bringing my levels down some?
Maybe 450ca and 9dKh?

I have been thinking that maybe some of the alk is percipitating out of the water column, so that may make sense to try and lowering my levels if you think it will help.

downbeach

08/25/2015, 12:17 PM

I used to keep my system around NSW levels, I didn't think there was any need to keep them any higher. I always had good growth and color, and wan't interested in any accelerated growth. So, my Ca was around 420, my alk between 7.5 & 8 dKH, and my Mg was at 1350 due to the level in my salt mix. I had dosers set up to keep my Ca and Alk, but didn't have to dose Mg since my WC's were enough to keep it at that level. I also dosed fully saturated kalk.

http://reefkeeping.com/issues/2004-05/rhf/index.php