Alk dropping ?

Ok, I am officially confused, I started dosing Kalk in my ATO to increase my PH and keep my parameters steady. My tank is primarily SPS.

For some reason my Alk has been dropping, from 10 to 8 to 6 over the past week and a half.

Any suggestions ?

Salinity 1.026
PH 8.4
Temp 79-80
Phosphates 0
CA 480-500
Alk 6 (currently)

 

Well sounds like you are using more alk them you are dosing with kalk.

 

Maybe, its a 90 gallon tank, 30 gallon sump. I started with 1tsp per 5 gallons RO/DI and now I am up to 4tsp per 5gallon RO/DI

 

Magnesium. Bet ya its really low.

 

+1 Test Magnesium.

 

Maybe I need to get a Mag test kit.

 

Not sure if I am missing something here. Don't get me wrong, you do need to be testing for magnesium if you are dosing, but if the magnesium was low, then how would the OP be able to maintain a calcium level of 480-500? It is not unusual for a SPS dominant tank to consume 1-2 dKH per day. Depending on how much coral you have, and how large it is, I have heard of peoples tanks consuming as much as 3-4 dkh/day. Calcium will drop more slowly (about 7 ppm per 1 dkh used), and magnesium will drop much, more slowly.

ALSO, as I said, magnesium drops very slowly. For example, steve wright once told me that he dosed 20 ppm of magnesium per month. That is only 5 ppm per week. If magnesium were the problem, you wouldn't have noticed such a drastic reduction in alk over a short period, like a week. This would be long drawn out.

I could also see water changes having an impact here.. What type of salt do you use? Also, do you thoroughly mix the dry salt in the container before scooping it into the freshwater?

From what I can see, you don't really have a problem here! You just need to dose more alk! I am not as familiar with kalk as I am with 2 part, so maybe someone else can give you some advice in that department

 

Magnessium for me does drop incredibly slowly, and I am not on my own there

RHF once commented that many people using some of the 2 part systems with some mag supplement in the calcium part , have rarely any need to dose additional mag

the relationship between Magnessium, Calcium and Alkalinity confused me for some time

basically, if Mag is not high enough, then some ions will fall out of solution, and those ions are carbonate ions hence Alk reduces

I also found out that the so called seawater ratio of Mag at 3 x Calcium level is not a gimme and that you can have really low Mag even if your calcium is high ( 600ppm Calcium can be achieved in a Mag level around 1200 ppm , but there is a good chance Alk will not increase above 7 in this scenario)

the relationship is often stated as "Magnessium helps to hold the Calcium and carbonate ions in solution"

the truth is more like "Magnessium helps to hold carbonate ions in solution if there are excessive calcium ones in it"

Kalkwasser delivers a balance of Calcium and carbonate
if your mag is low, then carbonates (Alk will be precipitating )

if your mag is not low, then you either started using Kalk when your levels where not ideal ( if you had 450ppm calcium and 9ppm Dkh then Kalk would keep them in a balance ratio)

if your calcium was high and Alk was low, then Kalk would just continue to support that unbalanced ratio

so you need to

check your mag and increase to 1280 min - 1400 or slightly over is OK
increase your alkalinity to 8 (higher is OK also somewhere between 7 and 11)

and once you have those levels balanced and within acceptable parameters
then Kalkwasser may be enough to maintain the levels

I also note Calcium indicated as 480 - 500
if it is possible that your calcium was over 500 ( that is the limit on many test kits unless you add more reagent so some people hit it and decide OK its 500)

so if it was 520 for example and your Dkh was 10

a fall to 480 along with a drop in Dkh of 2 is normal

the big difference is that a drop of 40ppm on calcium from 520 - 480 = nobody worries
but a drop of 8 - 6 on the Dkh = what happened there

yet the drop is balanced and all it means is that your Kalkwasser is either not at a strong enough solution and you need to increase it

or if your at full saturated , your evaporation is not significant enough to allow you to replace all your needs with Kalkwasser alone

and in that case 2 part dosing or a calcium reactor, either in addition to or instead of kalkwasser is your best option


or something like that?

 

Thanks for the input Gabby, I have used Coralife salt for two years, mix it thoroughly for 24 hrs before I do a water change, 20% every two weeks. And have always had CA of 480-500.

I have slowly been switching my tank to SPS over the past 6 months and figured my CA would drop eventually. Dosing Kalk for the past two weeks has raised and stabilized my PH and I was hoping would do the same for my ALK. I am at the low end of Kalk dosing, currently 4tsp per 5gallon RO/DI, that could go up to as much as 2 tsp per gallon.

 

Thanks Steve, very informative. I will definitely get a Mag test kit today so I at least know. And as I said above, definitely can go up on my Kalk dosing.