View Full Version : KH drop like a brick

10/30/2006, 08:09 AM
Hi Randy,

My tank is basically LPS and softies with 2-3 sps and 2 clams. I have the largest version of deltec CR and I notice i have to crank up the CR and run 12 hours a day in order to meet the KH demand and keep the tank stable at 7dkh.

Recently I visited a LFS, and they told me that it is actually doing more harm for the tank to crank up such high calcium level since I only keep LPS. My calcium is at least 450 ppm. The excess CO2 will drive the ph in the water to very low since the kh is only 7dkh.

He actually advised me to turn down my CR (since i don't need so much calcium), but to use seachem reef builder 3 times a week to maintain the kh at 9 or 10.

Is there any long term side effect if I use seachem reef builder to maintain kh without dosing anything for calcium other than the running of the CR?

How do people maintain kh at 10-11 dkh by using CR alone? My kh demand in the tank makes it virtually impossible to do so.

Please advise.


Randy Holmes-Farley
10/30/2006, 08:21 AM
My tank right now has about 450-460 ppm calcium, and it is just fine that way. I recommend 380-450 ppm, but even a bit higher is not a problem. If you did want to drop calcium, his suggestion is fine, but I wouldn't do it.

one thing to do is to ensure that the calcium and alkalinity are not being excessively precipitated as calcium carbonate, increasing apparent demand. To do that, ensure that the pH is not too high (unlikely here) and that the magnesium is not too low.

Do you know the alkalinity of the reactor effluent?

These articles may help:

A Guide to Using Calcium Reactors

Calcium Reactor setup calculator (CaCO3/CO2 reactors)

11/04/2006, 10:32 AM

Sorry for the late reply as I was away for work.

I did measure my effluent alkalinity and it was around 26dkh.

My question is, is it possible to have a reef tank that consume more kh than calcium. As a result, in order to maintain the kh using a balanced additive method like a calcium reactor, it became necessary to pump up the calcium reactor so much even though the excess calcium is not needed.

Another question is, is there any bad side effect if someone dose the kh addictive like reef builder on a long term basis, and use the Calcium reactor to maintain the calcium?


Randy Holmes-Farley
11/04/2006, 11:02 AM
My question is, is it possible to have a reef tank that consume more kh than calcium.

Not really in the short term,no. Either it is an illusion, an effect of putting too much dolomite in the reactor, or an effect of water changes with a high calcium mix like Oceanic. In general, if a reactor is meeting alkalinity demand, then it is also appropriately meeting calcium demand.

This article has more:

When Do Calcium and Alkalinity Demand Not Exactly Balance?