Ca-Alk balance and algae

[Willistein]

So, I've had my tank cycling for a couple weeks and right now I'm getting a slight diatom bloom. I've been monitoring Ca and Alk and have noticed a strange thing. The Calcium level has always been around 430-440, but the Alk level fluctuates quite a bit. I always thought that once the two were corrected they would stay pretty much balanced and drift lower together. For a couple days I'll dose Alk and get the level to around 8.5 or so. After only a day or two it drifts down to around 7.0.

Is this normal? My guess is that maybe the diatom growth is creating acid and is "using" the Alk. How stable should Alk be?

 

[Conesus_Kid]

I always thought the same thing, but in reality, even with a calcium reactor, they get out of whack.

 

[Gary Majchrzak]

water changes can throw the two off quickly but even without water changes they'll drift apart unless corrected.
It sounds "normal" that alk is being depleted quicker than calcium. Make sure to monitor Mg.

The addition of alkalinity supplements can boost pH greatly and that's the most important thing to avoid- a large swing in pH.

 

[Willistein]

It's strange though, because this tank is brand new and there is only coralline and a couple SPS corals.

 

[Gary Majchrzak]

actually

actually

it sounds normal to me.

Do you top off with kalkwasser?

 

[Willistein]

Yes, I'm doing one gallon every other night - which isn't all the topoff required. It's more like 2.5 gallons a day. Should I just start doing all topoff with kalkwater and see where it goes?

 

[Gary Majchrzak]

it's your call....

it's your call....

but I would.

It should definitely help slow down the depletion of alkalinity.

 

[mr.maroonsalty]

It's strange though, because this tank is brand new and there is only coralline and a couple SPS corals.

On some reefs coralline is the #1 reef builder. I have rocks that came home in a bucket that will no longer fit in one.
Alk is usually the limiting factor of any dosing regime; match your lime additions per the tanks alk needs, but be sure to add it slowly (a drip at a time is best) so your ph doesn't spike. You can match alk needs with lime by either dosing full strength material in a specific amount as you are now (x gallons per day/week), or simply adjust the saturation of the solution and match the addition of it to your evaporation rate with a drip. The later is much more ph friendly as far as stability is concerned.