Alk/Calcium dosing question

[Jasontkd]

I am using BRS sodium bicarbonate and Calcium chloride (prepared with RODI water) to dose my tank. I have followed the instructions and tested calculated the drop in both Alk and Calcium over a 5 day period to determine my daily dosing needs. According to BRS and several other things I have read, the dosing amount needed for both calcium and alkalinity should match. However, mine do not. I am needing far more calcium than alkalinity.

I even did another 5 day testing cycle to double check my results. I came up with the same result. My Alkalinity only requires about 3-4 ml per day. My Calcium is calling for 25ml per day.

I feel like I am missing something here because this doesn't seem right to me.

I am using Red Sea Alkalinity test, and Hanna Calcium tester. Also, I have tested my Magnesium and it is always between 1350 and 1400

 

[Randy Holmes-Farley]

Did you do any water changes during the 5 day? Water changes with a salt mix that does not match the tank is the main way that demand does not match.

How big of a tank are we talking about? The lower the demand (in, say, dKH per day) the more likely small effects will become significant relative tot he typically big and fixed demand of calcification.

If you are dosing nitrate or nitrate is declining, that will add alkalinity.

Tap water can add alkalinity and calcium.

It may also be that 5 days was not enough to properly gauge the calcium decline, which is likely close tot eh limit of error of most hobby kits.

It is OK to dose an off ratio, but I think it very likely that your measured ratio is not the real ratio taht you would observe over a month if you do not have the other sorts of issues I noted.

FWIW, there is no sink for calcium int eh tank that does not involved the balanced amount of alkalinity (2.8 dKH for each 18-20 ppm of calcium).

OTOH, there are ways that alkalinity can be added or subtracted without you knowing it.

 

[Jasontkd]

I have a 20 gallon waterbox. Actual water volume is roughly 15 gallons.

I did not do a water change in the middle of the 5 days. Both 5 day cycled I did the same way. I did my weekly water change. I tested my water. I dosed up to the levels where I wanted to be (9 dkh ALK, and 425 Calcium), and confirmed by testing again. Then I waited 5 days and tested again.

I use only RODI water with TDS of 0.

I am not dosing Nitrates. I am not sure what my current nitrate level is, but I could test that and report back. It has stayed pretty constant though.

I am not quite sure how to go about waiting longer to see what my decline would be. I do a weekly water change. I use Fritz Pro (blue box). I worry that waiting a month to see a more accurate decline would cause other issues in a small tank like mine. I would have to eliminate water changes, and my tank is an All in One and I do not use a skimmer.

 

[Randy Holmes-Farley]

IMO, the wait and see what drops approach is not best because the demand will depend strongly on the alkalinity. The daily demand is much higher at 10 dKH than at 7 dKH.

I would suggest picking your dose (whatever you want based on your tests, or guessing based on tank type) and then very slowly adjust calcium up or down as needed to maintain it. Alk can be adjusted faster as it changes faster.

FWIW, calcium levels are almost totally unimportant in the range of 400-550 ppm, so any value in that range is unlikely to make a noticeable difference.

 

[Jasontkd]

So, would you suggest just matching my Calcium dose amount to my Alk does amount for the time being?

 

[Randy Holmes-Farley]

So, would you suggest just matching my Calcium dose amount to my Alk does amount for the time being?

I don't think it matters much where you start, but I personally think your calcium demand is not really that high unless you have a lot of calcifying hard corals, coralline algae, or abiotic precipitation.

FWIW, if you are using my recipe #1 (that BRS uses) that contains sodium carbonate (soda ash) then those doses correspond to about 16 ppm calcium per day and 0.3 to 0.4 dKH per day in 15 gallons water volume.

The alk demand is perfectly reasonable, perhaps on the low side, for a tank without many fast growing hard corals or coralline algae.

How would you describe the tank creatures in this regard?

 

[Jasontkd]

My coral load is not really all that high, and my coraline algae is currently minimal. I have a mixed reef of zoanthids, a few SPS, and some LPS. I honestly can't imagine my demand is all that high based on previous tanks and experience. I have about 12-13 total corals in my tank, most still Frag plug size or just a little larger.

 

[Randy Holmes-Farley]

My coral load is not really all that high, and my coraline algae is currently minimal. I have a mixed reef of zoanthids, a few SPS, and some LPS. I honestly can't imagine my demand is all that high based on previous tanks and experience. I have about 12-13 total corals in my tank, most still Frag plug size or just a little larger.

Then expect the calcium may slowly rise at the higher dose you have, but that's OK. It won't rise so fast that you will have trouble adjusting downward in the future if needed.

 

[Jasontkd]

So, just to be clear, I should go ahead and dose 4 ml of Alk and 25 ml of calcium daily? Or dose calcium at 4 ml also? I just want to make sure I read you previous post correctly.

 

[Spieg]

FWIW - my 120 gallon was never very stable with equal amounts of 2-part. I was using a double line peristaltic pump (home made... single head squeezing both hoses) . Since this setup could only deliver equal amounts of 2-part solutions, this made it impossible to keep levels where I wanted them. I had to manually dose Alk each week to meet tank requirements. After a while, I just started adding about 10% more RODI to the calcium mix than the directions called for (watered it down a little) so I didn't have to babysit the dosing as much.

 

[Randy Holmes-Farley]

So, just to be clear, I should go ahead and dose 4 ml of Alk and 25 ml of calcium daily? Or dose calcium at 4 ml also? I just want to make sure I read you previous post correctly.

It doesn't really matter, if you start with the expectation that you will alter the dose after a week and see what the calcium level is trending toward (up or down or unchanged)

 

[Randy Holmes-Farley]

I should add that not all two parts are designed for 1:1 dosing (even some that claim it), and one should not assume that solutions have been made exactly as they are supposed to, or that dosing pumps deliver exactly what they are programmed to deliver.

 

[Randy Holmes-Farley]

I detail all of the known reasons for not requiring 1:1 dosing here:

When Do Calcium and Alkalinity Demand Not Exactly Balance? by Randy Holmes-Farley - Reefkeeping.com

 

[Jasontkd]

ok, i am REALLY confused. Based on this thread, on wednesday, I dosed my tank back up to optimal levels. Then thursday through Saturday, dosed 3.5 ml of Alk, and 10 ml of Calcium per day.

Sunday morning, I did a 4 gallon water change. Sunday night I tested my water and my Calcium was 500+ and my ALK was 18 dkh.

I am going to retest everything tonight in case there I did something wrong while running the tests. But, needless to say, I am pretty worried. All my corals look perfectly fine (aside from a frag of Blue Tubbs Zoa's that have been staying closed a lot more lately than they used to).

I just don't see how that can be correct unless I did something really wrong. If I confirm that the levels are that high tonight, I guess my only option is more water changes to bring them back down?

 

[bryanfuel]

Everything would probably be dead with a 18dKH. Is your test kit expired? Did you try test twice in a row and compare the results? Or maybe bring it to an LFS to test and confirm the levels for you.

Edit: after some googling, I guess you can have living corals with alk that high. TIL

 

[Jasontkd]

I assumed I would see a lot more issues in my corals if that was correct. I also figured since I had just done a water change that I made a mistake. I didn't have time to check it a second time, but I have been worried about it all day today at work.

I will check it when I get home and compare. My test kit isn't expired (that I know of). I have been using the same one for a while now, and it has been getting accurate readings prior to last night.

 

[Randy Holmes-Farley]

Everything would probably be dead with a 18dKH. Is your test kit expired? Did you try test twice in a row and compare the results? Or maybe bring it to an LFS to test and confirm the levels for you.

Edit: after some googling, I guess you can have living corals with alk that high. TIL

What makes you think everything would die at 18 dKH?

 

[Randy Holmes-Farley]

When you retest, also retest some new salt water to gauge the potential for testing issues as well.

 

[Jasontkd]

I am an idiot. I don't know what i did, but I did something wrong the other night. I tested multiple times last night and my Alk is 8.5 dkh. Mixed up some new water just to test the tester, and it tested at 9dkh. Calcium in the tank is 500. Calcium in the new water is 420.

So, apparently I was freaked out for nothing.

 

[Randy Holmes-Farley]

I am an idiot. I don't know what i did, but I did something wrong the other night. I tested multiple times last night and my Alk is 8.5 dkh. Mixed up some new water just to test the tester, and it tested at 9dkh. Calcium in the tank is 500. Calcium in the new water is 420.

So, apparently I was freaked out for nothing.

All's well that ends well.