View Full Version : problems raising calcium and low Mag

12/18/2011, 09:13 PM
Well I am having trouble raising my calcium level it seems to be stuck around 300ppm. I dripped about a half gallon of limewater last night and I have used an entire 8 oz bottle of kent liquid calcium over the last 4 days and it hasn't moved. I acquired a magnesium test kit from a friend today and i got around 900ppm. Over the last 2 days I have raised my alk from 6 dkh up to 8 dkh using baking soda and the previously mentioned 1/2 gallon of limewater last night. Earlier today I did a 20% water change and it didn't change any parameters.

My tank got out of wack from me being away from home for a few months and no water changes during that time.

My question is how much will raising magnesium up to say 1200-1300 change my calcium? Is there a way to calculate this or is it just trial and error? I have been messing around with the reef calculator and it says I have to use like 4 lbs of epsom salts to get it up that high but I don't want to take the chance of calcium precipitation by it spiking. I am also nervous about using limewater right now because the alk is rising much faster than the calcium.

My system is about 160 gallons of net water volume.

12/18/2011, 09:25 PM
Using limewater will add a lot of alkalinity along with the calcium. It's also very dilute, so it tends not to be very useful. According to the reef calculator:


the Kent Liquid Calcium should have raise the calcium about 40 ppm, which might be within the error range of your kits. I'd get a dry supplement, like Kent Turbo Calcium or a DIY equivalent, since they're more economical.

That magnesium level is low, and I'd probably do a series of 10-15% water changes, and work from there, since raising the level to 1300 ppm will take a lot of supplement. The calculator will give you some idea of the amount. 900 ppm is low, and I'd check some freshly-mixed saltwater as a sanity check on the kit. It'll take a fair number of changes to have a significant effect, depending on the levels in the saltwater. I think that you should be able to raise the calcium to a reasonable level even with the magnesium at 900 ppm.

Alkalinity at 8 dKH is fine and shouldn't cause any problems, so the tank is okay there.

12/18/2011, 09:44 PM
I took your advice and checked some new saltwater I have and it said it was about 1250 so I believe the test kit is accurate. Right after I posted the first time I checked cal again and it was 320 so it appears that adding 2 cups of epsom salt will actually raise my calcium by 20 ppm. Correct me if i am wrong but all mag does is make the calcium thats in the water available. That's why I am showing an increase in calcium by only adding magnesium sulfides. I am going to continue the water changes as well.

What I was saying earlier is that I am seeing a faster increase in alk than in cal using limewater so I think it's best to halt the use of limewater for now. I don't think it would be a good idea to have alk at 12 dkh when my cal is around 320-340. In the past I have always tried to keep calcium around 460-480 with the alk at 11-12 dkh and mag around 1400 with good results. At those levels my ph stays at 8.4 steadily. with my alk lower I have trouble maintaining ph any higher than 8.0-8.1

12/18/2011, 10:54 PM
Adding epsom salts will change only the magnesium and sulfate levels. The calcium won't rise. Magnesium does act to prevent calcium and carbonate from precipitating. That small a change in the calcium level is likely in the noise levels.

Kalk will raise the alkalinity level 2.8 dKH for each 20 ppm in calcium added, which is why you're seeing such a large effect.

12/19/2011, 10:23 AM
Ok very early this morning I tested my tank and calcium was still 320ppm and alk was 7 dkh which is a 1 dkh drop compared to yesterday evening. My ph also fell from 8.2 down to 8.0 overnight. After testing I added 2 more cups of epsom salt and waited about four hours and retested. While alk and ph were unchanged calcium rised up to 380. Mag tested at 1150. If the addition of magnesium was the only change then why did I again see an increase in calcium? If what you are saying is true this doesn't make any sense at all.

I'm not arguing I am just trying to figure it out. Only so much can be blamed on "noise" level.

I'm doing a little experimentation while I am getting my levels in check and I have been getting results I didn't expect.

Randy Holmes-Farley
12/19/2011, 10:59 AM
While alk and ph were unchanged calcium rised up to 380. Mag tested at 1150. If the addition of magnesium was the only change then why did I again see an increase in calcium?

That would likely be testing error. I mentioned that in your other thread as well. :)

Hobby kits are only roughly accurate. Don't try to over interpret small changes, and in some kits, even big changes are not to be trusted.

12/19/2011, 12:14 PM

Randy Holmes-Farley
12/19/2011, 01:58 PM

Good luck. :)

12/23/2011, 04:14 PM
OK, I am slowly getting my parameters in check but I have hit a wall. Calcium will not go above 360 ppm or so and alkalinity wont go above 7 dkh. I have been dosing limewater at about 1/2 gallon every night and now I am seeing precipitation on the rocks. I read that the addition of calcium could be causing the drop in alkalinity. But on the other hand raising alkalinity could reduce calcium.

Should I halt limewater dosing and add baking soda to bring alkalinity up first and then raise calcium with limewater? My pH is staying at 8.1-8.2.

What route should I take to get my levels correct? Due to my financial strains during the holidays all I have access to at the moment is epsom salt, kalk, baking soda, vinegar and calcium chloride. Using these products, what is my best route?

Could my use of granulated ferric hydroxide be causing me problems?

Randy Holmes-Farley
12/23/2011, 05:15 PM
I'd suggest dosing a two part in addition to the limewater. You can make a DIY two part with those ingredients.

An Improved Do-it-Yourself Two-Part Calcium and Alkalinity Supplement System