Matching Alk consumption with kalk?

[Mark75]

50g. sps tank mostly frags with a couple of mini colonies.

Over the last couple of weeks I have been letting my Alk drop from 10.5 dkh to my target of 9 dkh. This morning it tested at 8.9 dkh so I need to add a alk source.

I have two-part but would prefer to use kalk in my top-off water until demand exceeds what kalk can supply. I am cautious as I have experienced some issues with my sps due to high alk/low nutrients. I am using Reef Crystal salt and added to much kalk to my top-off water and my alk climbed to 11.5 dkh and my sps suffered. I have not added kalk over the last few weeks so my alk would drop to my target dkh of 9.

My tank evaporates around 4 gal. water per week and uses around .5 dkh per week(seems really low?). How much kalk should I add per gallon or should I just dose two part? I prefer to under shoot demand and adjust up than have my alk climb again.

 

[sinekal]

Two part is easier to make adjustments to your dosing in my opinion.

Kalk is just as almost as controllable if you run it through a kalk reactor with a dosing pump on a timer so you control how much goes in, but then you lose the convenience it offers if just adding it to your to off. The almost comes from the fact it doses alk and cal at a balanced rate, and in my case my water change raises my cal a little so I dose less cal than alk

 

[Randy Holmes-Farley Verified Community Expert]

Adding 1.25% of the tank volume in saturated limwater will boost the alk by 1.4 dKH.

You did not day how big your tank was, but for 0.5 dKH, you'd add about 0.5% of the tank volume, or 0.5 gallons per 100 gallons of tank volume.

I'd use less than saturated limewater and add more. Do not add that all at once.

 

[Mark75]

Adding 1.25% of the tank volume in saturated limwater will boost the alk by 1.4 dKH.

You did not day how big your tank was, but for 0.5 dKH, you'd add about 0.5% of the tank volume, or 0.5 gallons per 100 gallons of tank volume.

I'd use less than saturated limewater and add more. Do not add that all at once.

Tank is 50g. actual water volume. I use a 5 gallon water jug to fill my 5 gallon top off reservoir once per week, it typically has about a gallon left in it. How many teaspoons should I add to the 5 gal jug to maintain alk if my tank consumes .5 dkh per week?

 

[john.m.cole3]

From my understanding, 2 tsp of kalk per gallon equals a fully saturated solution. Randy stated that .5 gallons of a fully saturated solution would increase your alk by .5 dkh. So a half gallon of fully saturated solution would have 1 tsp of kalk in it. therefore the answer would be to add 1 tsp of kalk to your 4 gallons of top off water every week. Your dose will likely need to be adjusted as your demand for alk increases over time.

 

[Randy Holmes-Farley Verified Community Expert]

I agree that the dose is just a starting dose, which will require adjustment because limewater impacts pH and alk, and both impact the demand for alk.

 

[71xlch]

I aim for 8dkh. But if I'm 7.5 one month and at 8.4 the next I don't care. I watch for a trend and slowly adjust. Biggest mistake I have made reefing is trying to chase numbers. My tank wanders 7-8.5 over a period of a month. Sometimes up, sometimes down but stays in that range. With that I have had the best luck.

 

[Mark75]

I will start with 1 teaspoon per 5 gallon and adjust from there. I also have to determine how my 5 gallon weekly water change with Reef Crystals @11.5dkh will effect my alk. I plan on doing a water change this afternoon and will test before and after.

Thanks guys for the information!

 

[Randy Holmes-Farley Verified Community Expert]

A water change is the weighted average of the new and old water.

So if alk is 11 in the new water and 8 in the tank, a 10% change results in:

Final = 0.1 x 11 + 0.9 x 8 = 8.3 dKH.