Low calcium but alkalinity normal

[Buckyfan]

Hi, this tank is a downgrade from a 40 breeder with a sump. Now it is a 30 gallon without a sump but the whole system has been set up for at least a decade. Attached is a picture of my most recent water test. My calcium has been slowly dropping since I set up this 30 gallon tank ( about a month). I was not doing testing in the 40 breeder. I just have a few corals ( see pic). The goal of this tank is just to have some nice LPS and soft corals. I do a water change once a week ( RODI) with reef crystals. My specific gravity was a little low on this test which was 1.023. Coraline algae is starting to form. I have never dosed. In my reading it sounds like you dose calcium and alkalinity together, but my alkalinity seems fine.
My question is should I do anything? Should I just dose calcium? Should I dose the two part? My tank seems fine and my corals are happy.
THANKS

 

[Randy Holmes-Farley]

I don't think 265 ppm calcium can be accurate in a tank where you have not been adding alkalinity. There's nowhere for it to go.

If that is an LFS test, I'd suggest getting your own calcium kit.

 

[Buckyfan]

That's kind of what I was thinking too. There's not much to use the calcium. It's one of those chemistry machines at the local fish store so I figured it would be more accurate than what I have. I'll try to confirm that.

 

[Buckyfan]

So I just did the Red Sea calcium test and it didn't even get to the point where the scale started. I got to the endpoint with the plunger only going 0.4ml. 0.58 is 290ppm, so I've got to be less than that.
Seems consistent with the fish store. I was using tap water for a couple months at least in my 40 breeder tank before I switched it. Not sure if that could have anything to do with it?? My calcium has been slowly dropping based on a month of tests at the fish store though. Seems like a very small amount of titrant to get to the endpoint.

 

[Randy Holmes-Farley]

So I just did the Red Sea calcium test and it didn't even get to the point where the scale started. I got to the endpoint with the plunger only going 0.4ml. 0.58 is 290ppm, so I've got to be less than that.
Seems consistent with the fish store. I was using tap water for a couple months at least in my 40 breeder tank before I switched it. Not sure if that could have anything to do with it?? My calcium has been slowly dropping based on a month of tests at the fish store though. Seems like a very small amount of titrant to get to the endpoint.

Try that same test on some new salt water.

If it is actually low it can be easily raised, but it would be challenging to get it that low, even intentionally, in an operating reef tank.

Are you tracking alkalinity?

 

[Buckyfan]

Try that same test on some new salt water.

If it is actually low it can be easily raised, but it would be challenging to get it that low, even intentionally, in an operating reef tank.

Are you tracking alkalinity?

Ok I'll test it this weekend for my next water change. Yes I've been tracking alkalinity. I don't have those numbers right now. I'll post them this afternoon.

 

[Randy Holmes-Farley]

Ok I'll test it this weekend for my next water change. Yes I've been tracking alkalinity. I don't have those numbers right now. I'll post them this afternoon.

OK, sounds good.

 

[Buckyfan]

OK, sounds good.

Ok so I tested the calcium on fresh salt water and the calcium with my reef crystals was 325.
My alkalinity:
November 28th was 232, ca 292.
February 6th 261, ca 271
February 18th 203, ca 263
March 5th 186, ca 266
I've been doing water changes with reef crystals about every week to week and a half. It's a 30 gallon tank and I've been changing only about 2 to 2 and 1/2 gallons.

 

[Randy Holmes-Farley]

Ok so I tested the calcium on fresh salt water and the calcium with my reef crystals was 325.
My alkalinity:
November 28th was 232, ca 292.
February 6th 261, ca 271
February 18th 203, ca 263
March 5th 186, ca 266
I've been doing water changes with reef crystals about every week to week and a half. It's a 30 gallon tank and I've been changing only about 2 to 2 and 1/2 gallons.

That unusually low value for RC brings up three possibilities.

1. Low salinity. How are you measuring it and what do you think it is?

2. The kit is not giving accurate values, and calcium is higher than reported.

3. Least likely, the new salt water was a bad batch or a separated batch where it is different in the bucket top to bottom.

 

[Buckyfan]

That unusually low value for RC brings up three possibilities.

1. Low salinity. How are you measuring it and what do you think it is?

2. The kit is not giving accurate values, and calcium is higher than reported.

3. Least likely, the new salt water was a bad batch or a separated batch where it is different in the bucket top to bottom.

That salinity was 1.022. I guess I should've said that, sorry. I added some more salt to the mix and haven't changed the water yet. I can redo the test at 1.025.
Thanks for your help

 

[Randy Holmes-Farley]

That salinity was 1.022. I guess I should've said that, sorry. I added some more salt to the mix and haven't changed the water yet. I can redo the test at 1.025.
Thanks for your help

Was that in the tank or the new salt water?

Raising that to 35 ppt (sg = 1.0264) will raise the 325 ppm ca in the RC to 390 ppm.

 

[Buckyfan]

Was that in the tank or the new salt water?

Raising that to 35 ppt (sg = 1.0264) will raise the 325 ppm ca in the RC to 390 ppm.

No, just the new salt water that I hadn't used for a water change yet. I just saw on the bag that It had a chart of expected calcium levels given different specific gravities starting at 1.021, so I just tested it when it was at 1.022 because I was curious and impatient.

 

[Buckyfan]

No, just the new salt water that I hadn't used for a water change yet. I just saw on the bag that It had a chart of expected calcium levels given different specific gravities starting at 1.021, so I just tested it when it was at 1.022 because I was curious and impatient.

Also I'm measuring it with a refractometer that I did calibrate recently with calibration solution.

 

[Randy Holmes-Farley]

What is the tank salinity now?

 

[Buckyfan]

What is the tank salinity now?

The calcium of 265 was on my tank water which was 1.023. that was a week ago. I have not tested the salinity since then. I can do that today. I was going to try to slowly increase it with my next water changes

 

[Randy Holmes-Farley]

Ok, let us know how it goes.

 

[Buckyfan]

Okay, so I raised my water change fresh salt water to 1.024 and the calcium is 350. Is that even a little bit low?
I just tested the tank and it still comes up below the lower level for titrant. It turns blue after 0.4 CC's which doesn't even register in the test. Tank specific gravity is 1.025.

 

[Buckyfan]

So I did some double checking at the fish store with their chemistry machine. It looks like my tank calcium is higher than I'm testing at home and so is my water change. I guess I'll need to get a new calcium test. I currently have the Red Sea test kit. Is that a good one? Looks like the water change calcium is 419. I think that's acceptable. That's 1.024. My tank is 307 also at 1.024 which is still a little low but it's the highest it's been. Maybe I'm making some ground with water changes?. My last calcium was 263 at 1.025 in my tank.