Standard Raye of Uptake of Calcium to Alk

livinlifeinBKK

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Hey guys, I've been having an issue for a while measuring my calcium and not sure if it's me or maybe the test is slightly off somehow but could use some advice. I'll get to that part in a sec but first you should hear about this week...One of my tanks is a 10 gallon nano with only coral and inverts and over the past week I forgot to switch back on my ATO after cleaning and didn't notice that the tank water was evaporating a good bit which of course raised the salinity and stressed some of my corals. Today I realized something was wrong and tried to slowly add water to lower the salinity over a few hours. After getting the salinity right and also doing a water change I decided to test both alk and calcium because although I usually change water weekly it had been two weeks this time. This is where I'm confused. I tested alk before the water change and it was 7.6 which isn't far from my target of 8 I keep the tank at... calcium I also tested and it came in around 350 with a Red Sea kit. I also tested the freshly mixed saltwater I made and calcium tested at 400 (should be around 420, so maybe the kit that's always seemed to test low really does test slightly low) and alk was almost spot on at about 8.2 (should be 8).
Here's my question finally. The tank calcium usually tests around 375-380 so it would have had to drop 25ppm over two weeks with not a whole lot of coral and alk would have only dropped by around .4-.6 dKh. Does this sound proportional or do I likely have some testing error somewhere?
I should note that a couple corals which look very happy such as a cyphastrea I've had for a few weeks haven't grown much if any so perhaps there is a calcium deficiency?
Sorry for the lengthy post.
 

Timfish

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With hobbyest test kits there's always a good chance of test error. I prefer certain test kits but I have multiple test kits to compare against each other occasionally and when I get new test kits I test the old one against the new one. There's a lot of biology going on in tanks with biofilms and endoliths messing with sorbtion properties of substrates and other organisms using it so it doesn't surprise me you're seeing disporportional results. I would do somehting to verify test results some way but it doesn't hurt to add more alkalinity at 7.6 or 8.0 unless your results are way, way, way low.
 
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With hobbyest test kits there's always a good chance of test error. I prefer certain test kits but I have multiple test kits to compare against each other occasionally and when I get new test kits I test the old one against the new one. There's a lot of biology going on in tanks with biofilms and endoliths messing with sorbtion properties of substrates and other organisms using it so it doesn't surprise me you're seeing disporportional results. I would do somehting to verify test results some way but it doesn't hurt to add more alkalinity at 7.6 or 8.0 unless your results are way, way, way low.
First off, thanks for the reply!...As for the Alk, my salt mix should test around 8 at 35ppt so that's not my primary concern atm. I'm more worried about whether my calcium is just that low because if it is, I'm gonna need to dose calcium or maybe kalkwasser to see any coral growth if I'm not mistaken
 

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Just FYI corals use about twice as much bicarbonate as calcium carbonate and I worry more about bicarbonate. Yes, add calcium if it is low but I would try to verify test results someway. It would be nice if bicarbonate, calcium carbonate and magnesium carbonate all stayed in lock step but with all the biology going on we need to test each and be ready to supplement each individually if needed. (FWIW I never bother to test new saltwater. it's what's happening in hte system I worry about.)
 
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Just FYI corals use about twice as much bicarbonate as calcium carbonate and I worry more about bicarbonate. Yes, add calcium if it is low but I would try to verify test results someway. It would be nice if bicarbonate, calcium carbonate and magnesium carbonate all stayed in lock step but with all the biology going on we need to test each and be ready to supplement each individually if needed. (FWIW I never bother to test new saltwater. it's what's happening in hte system I worry about.)
That's what I was wondering (how much bicarbonate corals take up vs calcium)...that's really helpful to know...btw, the only reason I tested my freshly mixed water was to make sure it wasn't low in calcium for whatever reason and to give me a ballpark idea of the accuracy of the test since the parameters of a salt mix are written on the box
 
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Calcification by corals uses 18-20 ppm calcium for each 1 meq/L (2.8 dKH) of alk.
What would you advise me to do in this situation? I'm not noticing a lot of growth in my corals and my calcium is testing a good bit below 400. Again, it could be the Red Sea test kit but I really feel like calcium must be at least a little low which may be interfering with coral growth. My salt mixes at 8dKh which is usually considered plenty high...do you have any advice?
 

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What would you advise me to do in this situation? I'm not noticing a lot of growth in my corals and my calcium is testing a good bit below 400. Again, it could be the Red Sea test kit but I really feel like calcium must be at least a little low which may be interfering with coral growth. My salt mixes at 8dKh which is usually considered plenty high...do you have any advice?
I like to target 9dKH and 450 Ca in my tank. If you run 8dKH a target calcium of 425 would probably be best.
 

Randy Holmes-Farley

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What would you advise me to do in this situation? I'm not noticing a lot of growth in my corals and my calcium is testing a good bit below 400. Again, it could be the Red Sea test kit but I really feel like calcium must be at least a little low which may be interfering with coral growth. My salt mixes at 8dKh which is usually considered plenty high...do you have any advice?

If the values of either alk or calcium or both are below where you want them, I'd just dose them up, assuming you can get dosing chemicals. It's quite normal to need to dose.
 

Randy Holmes-Farley

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Btw, if my calcium really is as low as 350 could that harm my corals or would they just not be able to grow?

I'd boost it because I expect it is stressful for them to be too low in either alk or calcium.
 

Randy Holmes-Farley

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Btw, I was thinking of using the Red Sea Foundation A Calcium supplement and it says to try to avoid making contact with the coral when adding it but since it's a nano tank that might be difficult...how important is this?

Just try to disperse the concentrated cloud as much as possible. Maybe dilute it in the whole days evaporation amount. I think its a concern about salinity as much as calcium when dosing near organisms.
 
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