CA vs dKH - dosing 2 part

jkobel · Jun 24, 2017

Hi all,

Looking for thoughts and feedback on this topic. My system is a 75gal mixed reef (sps dominated) DT with a 20 gal sump and my tank has been up for about 4.5 years, it's very stable. I have been in the hobby for over 10 years but only in the last 6 months been dosing 2 part. When I test my water my levels are very consistent at CA = 375-380 and dKH = 8.2-8.4.

I am not able to set up my dosers yet (waiting on the Vertex Cerebra to get to beta v2 - those of you on the member boards know that story) so I am testing once a week and dosing as needed.

Every week my results are virtually identical to above testing with Red Sea.

I use the BRS calculator to figure out my dosing and the suggested calcium dose is always in 12-13oz range while my alkalinity is always in the 3-4oz range.

I have been told many times that I should be dosing the same amount of CA and alkalinity but I admit I am stumped. I have been averaging the recommended doses because otherwise either my calcium would never get to 420(ish) or my dKH would spike to around 13.

Do you folks see readings that are this far off and what do you do when dosing to account for this? All input/feedback welcome.

Thanks!

john.m.cole3 · Jun 24, 2017

Before we go any further, what is your mag level?

What are your target levels i.e. 8, 440, and 1400

jkobel · Jun 24, 2017

Mg is 1280 and is pretty consistent. I have not yet dosed Mg so I have mostly been just watching it to see how it changes over time.

Targets are 9, 420 and 1400.

john.m.cole3 · Jun 25, 2017

Ok, cool. Mag is on the low end of the spectrum but not so low that it will mess with the alk/cal balance. And a balance is what you are facing. Alkalinity and calcium have an inverse relationship so balancing them takes lots of testing and tuning. I would work things in an order beginning with magnesium. I say approach mag first b/c you can raise it quickly, and it will ensure stability between your alk and cal. 100 ppm/day is a safe rate to raise your mag. Next is calcium. You can raise it by 50 ppm a day. Raise it up 50 ppm on the same day you raise magnesium. Test the next day. You should see a rise in mag and cal and a drop in alk. That's normal/ Continue to test and tweak dosing until you get it close to being equal parts dosing. Equal dosing is recommended comsidering the inverse relationship between alk and cal.

jkobel · Jun 25, 2017

This is great feedback. Would I just use the magnesium mixture that is part of the two-part? I ask because the directions say to dose the whole container when you finish dosing the CA/alk.

Would I just use the calculator to get the dose to raise by 100ppm/day until I get to 1400? (supplementing the CA as you indicated?)

Randy Holmes-Farley · Jun 25, 2017

I do not know what you are dosing to know if it is even intended to be balanced, but the main way that balance is off is due to salt mixes not matching the tank, so water changes mess with the levels. What salt mix are you using for water changes?

Also, balanced dosing will not be able to raise calcium without alk getting too high. Boost calcium to your target with just the calcium part, and then resume balanced dosing and see what happens.