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FAQs on Calcium and Alkalinity in Seawater, Measures, Testing  

Related Articles: Calcium and Alkalinity Explained by Anthony Calfo, Calcium, Biominerals, The Use of Kalkwasser by Russell Schultz, Calcium Reactors, Marine Maintenance, Marine Water Quality, Magnesium in Seawater, Strontium in Seawater, pH, Alkalinity, Marine AlkalinityLive Sand, Marine SubstratesReef Systems, Refugiums

Related FAQs: Ca/Alk 1, Ca/Alk 2, Ca/Alk 3, & FAQs on Calcium & Alkalinity: The Science of Calcium & Alkalinity, Importance, Sources, Use of AdditivesTroubleshooting/Fixing, Products, & Calcium, & FAQs on Calcium: Rationale/Use, Calcium Measuring/Test Kits, Sources of Calcium, Calcium Supplements, Dosing, Chemical/Physical Interactions, Troubleshooting/Fixing, & Calcium Reactors, & FAQs on Calcium Reactors: Rationale/Use, Selection, Installation, Operation, Media, Measuring, Trouble-Shooting, By Makes/Models, & pH, Alkalinity, Marine Alkalinity, Marine Alkalinity 2, Marine Alkalinity 3 Marine Supplements 1,

Not test "strips"... neither accurate nor precise.

Calcium testing... Same gear for spas?    7/9/14
Hello WWM Crew,
Thanks for all the info on this site. I use this info all the time and now I have a question that is not related to aquariums. I bought a house last fall and it came with a hot tub. Now not only do I have to test my saltwater aquariums I have to test my hot tub. I am told that I have to test for calcium hardness and it should be between 200/300ppm. Is this the same calcium that we test for in reef tanks?
<Yes it is>

And I would like to know if my Salifert calcium test kit can be used to test my hot tub calcium level.
<Yes it can be>

Would it give an accurate reading having Chlorine in the water?
<Mmm; as far as I'm aware, yes. A simple test on your part... adding some chlorine to a tested/known sample of water... could ascertain whether this is so>
Again, thanks to everyone who puts their time and effort into this site.
<Welcome. Bob Fenner>

Calcium and KH/Test Kits 9/12/11
<Hello Caz>
I recently picked up a new API Reef Master Test Kit. When I tested my water it came back at Calcium-600ppm, KH-15%.
<%??. No such thing as a percentage factor. Likely was dKH.>
Both these seem very high. I've just started using Instant Ocean Reef crystals. Honestly all I used to test for were the big 3, Ammonia, Nitrites, and Nitrates (I know-shame on me). Was wondering if that's too
high for my reef tank (Zoas, Frogspawn, Torch, Hammer, Galaxea, Acans, Blue cloves, GSP's, and one Toadstool). If both of those are too high, how do I lower them to recommended ppms and any thoughts to why they would be o high?
<They are high and with a dKH of 15, I'm surprised you are reading 600ppm calcium. I'd retest for calcium and follow the instructions to the letter.
If it's the same reading, take a water sample to your LFS and see if they get similar results. As far as lowering these levels, weekly water changes should slowly drop these levels. Obviously you do not want to add calcium or buffer supplements during this process.
James (Salty Dog)>

28/01/2010. Safely Increase Calcium & Alkalinity  1/29/10
Morning Simon,
<Good Morning Beth>
Thank You for the response Simon. I should have been more clear about the color tests, they do not record a zero phosphate/Nitrate level. Their lowest color recording is 0.20 mg/L for phosphate and 10 mg/L for Nitrate.
<?Really? Your phosphate should show as a minimum 0.03ppm, and you should be able to measure nitrate more accurately than 10ppm also>
The phosphate color test was clear, to my eye, <ok> but without a color chip to determine 0 phosphate or even 0.1 phosphate, I wrote that it was less than 0.2 phosphates. The Nitrate test that I performed did have a slight yellow tint result, but again it was not the exact match to the lowest Nitrate color chip provided which is 10mg/L. Which is why I stated that it was less than 10 mg/L.
<I do encourage you to re-read the instructions to determine if there is a more accurate way of determining results with these. I also encourage you to purchase Salifert for these two tests in future>.
The only test that I can be positive about is the alkalinity, because it has to be titrated from blue to yellow green.
Even their Calcium test is subjective, to me, because of their use of the word blue as the end result color. I'm supposed to titrate to a blue color. To me the endpoint is violet. I performed the test four times. Titrated to 3 different color changes, a deep purple, the next to a violet, the next to a blue. To reach the blue color, I had to use an obscene amount of titrant and the numbers ended at over 1000 mEq/L.
<Check the date on your test kits>
So using my 3 vials as a color reference, I titrated the fourth test to a violet color which gave me the result of 480meq/L.
I hope I did not confuse the heck out of you.
<No, I understand well here.>
I need to invest in beakers, stir bars and a Mettler stirrer. Almost half joking, but at the least, I should invest in a more accurate marine test kit.
<Agreed. I would use Salifert here for all of these tests instead of the 'Instant Reef'>
Thank You
<No Problem, Simon>

Reef - Additives/ Testing WWM, Hello.  <Howdy, Steve Allen tonight.> I finally received my Salifert Calcium, Magnesium, and KH/ALK test kits. <Good, it's best to supplement only what you have tested and found deficient.>  Here are my results: Magnesium- 1410 KH/ALK- 16 dKH Calcium- 450 I also tested last week with slightly lower calcium.  I added SeaChem's Reef Advantage Calcium to raise it slightly. <450 is good.>  Also seems good to me. (3X the Ca is a good number.> About the ALK....HOW DO I LOWER IT? <Water changes, nothing drastic. Follow Scott's guidelines & things will normalize. See here:   http://www.wetwebmedia.com/scottsh2ochgart.htm> It seems WAY to high? <Actually not terrible as range should be 8-12 dKH.> A few weeks ago (before I had test kits) I added two capfuls of SeaChem's Reef Carbonate, which I believe caused the tank to become very cloudy.  Could this cause the extremely high dKH? <Possible; you certainly don't need to be adding more at this point.> For additives I have SeaChem's Reef Advantage Calcium, SeaChem's Reef Builder, SeaChem's Reef Trace, and Epsom salts. <A better way to replenish these trace elements is Scott's water change regimen.> I have only added a small amount of Reef Advantage Calcium to raise the calcium slightly.  I have not used the Reef Builder or the Epsom salts. How often should I use the reef trace?  <see above> I have a feather duster, toadstool leather, polyps, mushrooms and 80 lbs of HI rock/ live rock in a 75 gal tank. <No big calcium consumers here, so you won't need much supplement. Again test periodically and supplement only that which runs low.> Also, I am considering upgrading my lighting to Custom SeaLife Power Compact with Moon-lite 4x65. <Nice unit. I love mine.> I can't afford VHO, and this seems like a good alternative? <How big is the tank? What do you plan to have long-term?> Thanks

- Stabilizing Calcium/Alkalinity - Thanks for the reply. <My pleasure.> I apologize for the many questions that follow. <I'll get over it.> Yes I have read the article on "Understanding Calcium & Alkalinity" and there was some confusion. I have noticed many aquarists stating on their websites too have both very high calcium levels as well as high levels of alk in their tank water. Am I right in assuming that this is an unstable situation and that this would require constant monitoring? <That is a good conclusion.> How do you get both levels so high? <Jam the stuff in there.> Because that is what I was trying to do, thinking that it is a good thing. <Yeah, many people 'think' it's good, but honestly, alkalinity and calcium are nowhere near that high in the wild - somewhere closer to the middle of the scale.> In my current tank state should I continue doing water changes until calcium levels have dropped to below 400 ppm? <400ppm isn't dangerous - in fact, that's fine.> Do I then need to test both calcium, Ph and alk, <I would...> from previous experience I assume that the alk will be low. <You are probably right.> Would I then need to raise the level of alkalinity until the system is in a balanced state? <I think you could probably raise the alkalinity without necessarily dropping calcium below 400 ppm.> i.e. both calcium & alk in the middle of the scale or alk high and calcium low or visa versa, is this correct? <Both in the middle of the scale would be best.> I understand that the level of alkalinity represent the buffering capacity of the water? And it's ability to resist changes in the PH level? <Yes - both are the same - buffering capacity is the resistance to pH changes.> Would it then not be better to keep the alk level high? <Shoot for the middle.> Calcium on the lower part of the scale? <Same here.> If so, what is needed to raise the alk level without affecting calcium and ph. <Lay off the calcium for just a little while - the chemical processes in the tank are inter-related so that some of the required calcium will come out of your substrate and live rock.> Do I need to get to a balanced state. before starting Kalkwasser or liquid supplements? <I would.> (Cannot afford a reactor now - also have mostly soft corals so demand is not that high) or will Kalkwasser or 2 part supplements do it? <Two part systems and Kalkwasser will do nothing for your alkalinity, so... I would work on that first.> Could you also venture a guess as to why the tips of the algae (Halimeda/Caulerpa) turn white/translucent, the base of the blade is a healthy green? <Could be a couple of reasons - this is typically the area where new growth occurs so that could be one explanation. Could also be due to water chemistry.> Your insights will be appreciated. Cheers Hilton <And cheers to you, J -- >

- Calcium & Alkalinity Tests - Hi Crew, <Greetings, JasonC here...> I have a question (or a few) I have had my reef tank set up for about 5 months. There has not been to much coralline algae growing in the tank. I purchased a Red Sea calcium and alkalinity test kits. Are these good kits?? <I'm not sure... I've never used them.> For the life of me I cannot determine alkalinity with this kit. It only has low, normal, and high on the side also has mill/eq. <Millilitre Equivalents [mill/eq] should be sufficient to get a reading... multiply the number you get by 2.8 and that should give you the dKH reading.> I tested my calcium with the same brand kit and it was 350. alk was somewhere between normal and high. I've added some Kent dKH buffer and over the last few days I've noticed small patches of darker purple coralline all over the glass. I am not sure when I should stop adding this Kent dKH buffer. I have been adding daily for the last four days. <What do the instructions say?> Can I assume that because coralline is appearing that the water conditions are starting to get better???? <I wouldn't jump to that conclusion myself... the conditions may have been right all along.> I also have a bottle of Kent liquid calcium can I add this to increase calcium levels or should I not. I was told by my LFS that I would be better throwing it in the trash that putting it in my tank. <I would agree... you're best bet for supplementing calcium are the two-part systems, like ESV B-Ionic.> Please excuse my ignorance I need help. <Here's your chance to educate yourself - read this article: http://www.wetwebmedia.com/calcalkmar.htm > Oh ya one more question. My Red Sea calcium test kit reads calcium in increments of 50. Directions say for every drop of reagent this counts as 50. I added 3  plus 4. which would be 7x50=350. if this only measures on increments of 50. Will it give the same reading if calcium is 310 apposed to 345. <That's a question for Red Sea... in the mean while, consider the Sera test kits as they have a much finer granularity.> thanks ??????? I need serious help. Should i stop adding these supplements? I am afraid that if I add to much and alkalinity gets to high my tank will have a snow storm. <Your numbers aren't that high, but I would for certain read that article so that you will have a better understanding of what's going on here and the relationship between calcium and alkalinity.> Thanks so much for all your help. Chris     I had to write this quick sorry for the mess <Cheers, J -- >

- Alkalinity Test and Kalkwasser Dosing - Thank you for the prompt reply! <My pleasure.> I have an alkalinity test on order so hopefully this will provide some additional clues soon.  Actually I do have test strips that include an alkalinity test but this reading has always been off the chart (I think this particular test on my test strips is intended for freshwater only).  I quit using test strip soon after I setup my aquarium because they were too difficult to interpret and I questioned the accuracy.  <Strip tests are notoriously inaccurate.> The alkalinity test I have ordered is from SeaChem.  What is your opinion on SeaChem tests? <Should do you just fine.> My main curiosity now is regarding your original reply - you said my Kalkwasser use is not optimal.  When I said I use Kalkwasser in all of my makeup water, what I meant by this is my makeup water is made by dissolving 1 tsp of Kalk in 1 gallon of RO water, then pouring-off the clear solution into a makeup water container, from which I add approx 1 - 1.5 gals/week to my main tank.  To me this sounds like the same approach you mentioned. <Same but different... unless I misunderstood your top-off method. Typically, well at least in my tank, the top-off water sits for days and days before the container needs to be refilled. Kalkwasser won't work like this because it will settle out of solution - it needs to mixed and used within 12 hours or so.> Does my clarification help or did I misunderstand your description of optimal use of Kalk? <Perhaps we are both misunderstanding something...> I have read about adding acetic acid to the Kalkwasser mix to enable higher levels of Ca to be dissolved ( http://www.reefscapes.net/articles/breefcase/kalkwasser.html ).  Is this more of an optimal use of Kalk? <Uhh... not in my opinion. Even though acetic acid is weak, you can still do some harm to the buffers in your system, and once they are gone, they're hard to get back. Do read though our Kalkwasser FAQs, as I do believe Anthony Calfo lays out his "slurry method" which I think you will find useful. Also, here's another article for some background: http://www.wetwebmedia.com/calcalkmar.htm > Greg <Cheers, J -- >
- Alkalinity Madness, Follow-up -
Well, here is the FAQ - "Alk/Calcium Hi gang, hope everything is groovy. My alkalinity reading is 60 mg/l (I'm using a Hagen test kit). Does that mean ppm? What is the conversion equation for dKH or meg/l? (sorry, I've never tested Alk in the past).  Also I can't seem to get a reading on my Calcium (readings are indicating sky high, which is improbable) as I use a Hagen test kit for that also. Is there a better/best kit? Thanks, you guys rock..  Justaguy < Hey Justaguy!  Craig here, and feelin' groovy.  The equivalents between measurements is as follows: 1mg/L = 0.02meq/L  Americans measure alkalinity in meq/L  The German hardness scale is dKH. So, at 60mg/L X 0.02 = 1.2meq/L. so using the measurement you got from the Hagen kit your alk is 1.2meq/L VERY LOW.  Most keep calcium around 425-475 calcium and Alk at 3.5 to 5 meq/L (1mg/L=0.02meq/L). Also test pH regularly as well.  I suggest purchasing quality test kits to ensure accuracy.  Salifert and Seachem are two excellent brands.  Have Fun!  Craig>" So, again, following these guidelines, my alk. would be 3meq/L, is this right? <It was my understanding that your test kit was measuring KH [carbonate hardness] which is 1:1 to dKH [German carbonate hardness]... does your kit measure in some other unit?> There is a difference between meg/L and mg/L right? <Yes.> How are you getting 54ish?? <By converting from 150 KH.> What is the correct formula. <Not sure - I use an online calculator because I just don't have time to do anything else: http://www.saltyzoo.com/SaltyCalcs/AlkConv.php> How could I possible have 54ish? <Again, was working on the information you provided which said "I dropped 15 drops to color change.  Kit says, to get KH, multiply number of drops by 10." - that's KH, same as dKH which is what I plugged into the calculator - I could have misunderstood, it wouldn't be the first time.> Thanks crew!  Micah <Cheers, J -- >

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