Adjusting levels when kalk dosing

[rhdoug]

I have a 15 year old 58 gal mixed reef which I have always dosed with 2 part and Mg. A month ago I switched to kalk dosing (Mrs Wages) due to low ph, the tank rarely was able to get itself above a reading of 8.0. Since the switch, the ph has greatly improved, with a lows of 8.0 and high readings varying from 8.12 to 8.2 on most days.

Today's tests showed that:

Ca has been steadily climbing, from a reading of 400 a month ago to 460 today.
Alk shows a slight increase : dkh was 10 a month ago and 11 today.
Mg has always varied between 1380 and 1500, and continues to do so. Currently 1500.

I use approx 9-10 gallons of top-off a week, and have been mixing the max. 2 tsp of lime per gallon in my 10 gal top-off tank. The top-off is delivered via a litermeter.

1. While not overly concerned about the Ca, do you think I should back off a bit on the mixture ratio? I don't want to lose my ph levels.
2. Also not a big concern, but there is a lot of sediment accumulating at the bottom of the tank, which I know is not a huge concern, but how often do I need to clean the reservoir out?

thanks,

 

[Nano sapiens]

Since Kalkwasser (Limewater) is a balanced additive (has the same ratio of calcium to alkalinity used by calcareous reef organisms) you would normally be seeing a much higher alkalinity rise with calcium going up that much.

The accumulated residue in your chamber is mostly precipitated calcium carbonate which drives alkalinity downward in relation to calcium. The general recommendation is to remove all residue in the chamber at least every 2-3 times that you add lime.

I create a saturated solution of Kalkwasser in a separate container. Since lime is so inexpensive, I clean out the residue each time before I make a new batch of Kalkwasser.

 

[Randy Holmes-Farley]

Gauge the dosing of limewater (kalkwasser) on the alkalinity. If the calcium actually gets too high, look to use a lower calcium salt mix. 460 ppm is fine. I wouldn't worry unless it got above 550 ppm.

Calcium will very slowly rise with limewater because of magnesium getting into the calcium carbonate in place of calcium, but the effect is slow and water changes usually limit it. It's a good reason to use a salt like normal IO when using limewater, rather than the ones that start excessively high.

I clean my reservoir once every 2-3 years.

 

[rhdoug]

I am due for a small WC. I have a bit of reef crystals left but as fate would have it I mistakenly ordered regular IO last time so I will switch back to that.

So keep to the 2 tsp/gal then?

 

[Randy Holmes-Farley]

Since alk is seeming to go up, I might drop back to 1 or 1.5 tsp per gal and see what that does to alkalinity over a few days.

 

[Nano sapiens]

I clean my reservoir once every 2-3 years.

Interesting. Maybe I've been too fastidious

Is it safe to say that the precipitated calcium carbonate has only a mild effect on the calcium/alkalinity ratio?

 

[bertoni]

The precipitation has no effect on the calcium-alkalinity ratio. Limewater contains calcium and alkalinity at same ratio as calcium carbonate.

 

[Nano sapiens]

The precipitation has no effect on the calcium-alkalinity ratio. Limewater contains calcium and alkalinity at same ratio as calcium carbonate.

I had to rethink what I thought I knew and I believe you are correct. Calcium carbonate precipitating out in an aquarium would cause a drop of both calcium and alkalinity in the standard cal/alk ratio. Thanks for the correction.

I had to go back re-examine the reason(s) given to remove the precipitate. Sprung and Delbeek's 'The Reef Aquarium Vol 3) provides a good explanation.

'Old kalkwasser typically has precipitated calcium carbonate settled on the bottom of the container. If this white powder is dosed into the tank with Kalkwasser, the high pH around the calcium carbonate particles floating in the water will cause further precipitation of calcium carbonate onto the particles that act as nuclei for crystallization. Use fresh kalkwasser only, or periodically remove the accumulated precipitate from the kalkwasser reservoir.'

 

[tmz]

1. While not overly concerned about the Ca, do you think I should back off a bit on the mixture ratio? I don't want to lose my ph levels.

If you reduce the amount of calium hydroxide you dose it will not raise pH as much. I wouldn't worry abut 460ppm calcium. 11dkh is ok ; I like ity around 9 or 10 betterthough, personally.


2. Also not a big concern, but there is a lot of sediment accumulating at the bottom of the tank, which I know is not a huge concern, but how often do I need to clean the reservoir out?

Clean mine less often than Randy. I jsut scoop out precipitants when they get deep enough to be close to the dosing intake tube.

 

[tmz]

Abiotically precipitated calcium carbonate is the same as calcium carbonate precipitated bioticallly in terms of calcium and carbonate ratios.

The undissolved calcium hydroxide doesn't float around unless it's stirred up. Stirring it back in when refilling the reservoir is no different than adding new powder.

 

[rhdoug]

...The undissolved calcium hydroxide doesn't float around unless it's stirred up. Stirring it back in when refilling the reservoir is no different than adding new powder.

Ah, I wondered about that. Since I mix directly in the 10 gallon tank reservoir, and there is precipitate on the bottom, it is likely that the concentration of lime in the top off water is more than what is added as new, correct?

 

[bertoni]

That's possible if you've added more than the saturation limit (2 tsp per gallon) in the past. A lot of the precipitate might impurities and calcium carbonate, though.

 

[rhdoug]

That's possible if you've added more than the saturation limit (2 tsp per gallon) in the past...

It is very likely that is the case. I'm pretty sure a few of my tsp's were "heaping" or at least rounded. I may rinse it out next week when it's empty and start over with more careful measuring next time around.

 

[Randy Holmes-Farley]

No need to rinse it out every time. Just leave it there and let it settle out next time too. There will always be precipitate of calcium carbonate, magnesium hydroxide and other stuff, but some of it may well be usable calcium hydroxide.

 

[tmz]

I always add a little extra over the 2tsps per gallon since I dose at that level. If you wan't to precisely controll the dose to a lesser amount , the extra undissolved calcium hydroxide could throw that off a bit depending on how much you have in there.

Personally , I'd keep the reservoir at full saturation, ie 2 tsps per gallon and not worry about the extra useable calcium hydroxide. I'd control the dose by putting a timer on the liter meter 3 ,turning it off for a percentage of the time to get the 24 hour dose I wanted( e.g. for 75% time it off for 6 hours, probably during the day). This requires an additional top off with ro/di though for the missing 25%. I did this years ago when I was using limewater and a CaCO3 reactor and balancing them off.