[kevinpo]

This week I'd like to discuss Calcium and alkalinity levels for stony corals.

Natural seawater (NSW) runs about 400 ppm of calcium and 2.57 meq/L for alkalinity.

I have run different systems over the years from 400-500ppm calcium and 2-4 meq/L alkalinity and IME elevated levels have not produced substantial growth rate increases. Calcium levels can run quite low (200ppm) and if alkalinity is kept at or above NSW levels growth continues normally. However if alkalinity drops below NSW levels growth slows dramatically even when calcium is kept at or above NSW levels.

I have found that it is easier to maintain calcium and alkalinity levels closer to NSW than at elevated levels. At elevated levels they tend to swing up and down more rapidly and can cause build up of calcium on pump impellers and heaters.

At NSW levels I expect about 1" a month growth on average.
Although there are several other factors for stony coral growth, proper calcium and alkalinity levels are essential for growth. The purple coralline algae that many people desire to cover their rockwork also require that calcium and alkalinity levels be maintained properly.

I test for both about once a week and record the data, which can be viewed here in my Personal Online Aquarium Log.

Please feel free to add your experiences and comments.

Regards,
Kevin

[Reefland]

Kevin,

Ironic that this is a very relevant topic in our current situation. Over the past several months, I have noticed a significant decrease in growth on most of our corals. Our Acropora spp. have for all intent purposes stopped growing and out Montipora spp. have slowed significantly.

I thought that it was due to not being able to meet the calcium demand in our tank, which was surprising but a theory since we have been able to maintain calcium and alkalinity levels appropriately since day 1 using Ocean Blend 2 part additive. I started thinking about dripping limewater to see if there was a change in growth so I obviously tested the CA and ALK before starting this. To my surprise throughout Christmas when I was working 1,000,000 hours a week, our CA and ALK have become out of balance. Using Salifert kits, the ALK was at 2.3 mEq/L and the calcium was over 500; this was just 2 days ago. I began to adjust the 2-part addition immediately by halting any calcium addition and only dosing the ALK/pH addition. Yesterday CA still measured over 500 and ALK was at 2.4 mEq/L. Due to other problems, I have yet to start dosing limewater.

What I am getting at is I now beleive that I was able to meet the calcium demand with the 2-part additive, but got out of balance and therefore stopped calcification in the Acropora spp.. My hope, and I will report, is that getting these back in balance with the 2-part additive and then maintaining using limewater and soon a CA reactor will allow calcification to begin again and we will start seeing the growth.

[charlie]

Scott,
What I have been using to keep the alkalinity in balance is baking soda and washing soda in a 6 to 1 ratio. I do not use a calcium reactor, and on Kevin's advice, started using these as a buffer. It works for me. Hope you get everything back in balance.

[Reefland]

Hi charlie,

A friend actually sent me some quotes from Randy Holmes-Farley today from an article he wrote talking about the same thing. I think the issue here is I just got pulled away from the tank due to work and lost track of it. The second problem is I made assumptions that for so long the calcium and alk was balanced and since we didn't change the dosing routine, it would still be the same. Bad assumption huh?

[charlie]

I can't tell you how many times I have been guilty of the same. And that's when the tset kits are right in front of my nose. I think it just goes to show how much we seem to take for granted, and sometimes how really wrong we are!!! That is what is fun (?) about this, it always seems to catch you a little offguard.

[Reefland]

Yeah but it sure is aggrivating to let something like this get out of control. As mentioned above we have observed a near complete stop in growth in our Acropora spp. frags. The important thing it to find the problem and correct it I guess.

[dougc]

I have been running near-NSW levels of both calcium (410-420) and alk (7-9 dkh). My tank has been running about 9 months now and I have not really seen explosive growth in the 1" per month range. I know with my last tank, growth really didn't take off until the tank had been running for about a year. I am running a calcium reactor and a kalk reactor. Without the kalk, the pH was dropping pretty low. It has been stable since I added the kalk reactor. I think that my alk stays a bit on the low side because I am using Oceanic salt, which runs lower than some other salts.

I am trying to be patient and not tinker too much. Pushing alkalinity too high has been anecdotely associated with RTN events. I have some baked baking soda handy to tweak my levels if necessary, but I haven't needed it yet.

[charlie]

One thing is for sure. Nothing good ever happens fast in a reef tank, I learned that the hard way. Scott, don't beat yourself up to bad, it hurts too much , I'm sure your levels will get back to acceptable with a little TLC.

dougc, I got real lucky to have a guy around me who really knew what was going on. I attribute much of my luck to a good pair of ears and alot of patience.

[kevinpo]

QUOTE]My tank has been running about 9 months now and I have not really seen explosive growth in the 1" per month range[/quote]
You might want to test your phosphate levels. High phosphate levels will inhibit SPS growth, as will high levels of DOC's. I also use Oceanic salt and find the alkalinity levels low but calcium and magnesium levels are 480-500 ppm and 1300ppm respectively. It is easier and less expensive to bring alkalinity levels up than calcium and magnesium.

I haven't found that low PH (7.8 - 7.9) to slow the growth or cause other problems with corals. You can use just sodium carbonate (washing soda) to raise PH but be careful to add only small amounts at a time, as it is very powerful. IMO running both the calcium reactor and Kalk reactor is the way to go and you should see some good results soon.
TIP:
If you run the output of your Kalk reactor into the intake of your skimmer it will help to remove phosphates from the water.

HTH,
Kevin

[dougc]

No measurable phosphates, but I don't think that is always a reliable indicator that a tank is free of phosphates. The algaes in the refugium and the main tank probably soak up any free phosphates, leaving nothing for the poor test kit.

The only thing worse than no growth is rampant growth. I might end up like Gene, taking a machete to my corals to keep them from growing through the ceiling.

[charlie]

yeah, rampant growth would kill me!! I gave up on the machete, now I just use a hedge trimmer