Natural sea water alkalinity observations

[Fastmarc]

Hi all,
I went and got some fresh sea water to do a water change and decided to check the ph and alk readings. The water was collected at 8:30am, tightly sealed and carried home (15 mins). The ph (via pinpoint) was 8.13 and the alk measure (salifert) 6.1 dKh. I couldn't measure the calcium as I have problems seeing the colour change and require assistance.
Doesn't this alkalinity seem a bit low and apart from the test kit being faulty, why would this reading be this low.
By-the-way, I'm in Jamaica (caribbean) and the specific gravity of the water is usually 1.026 (pinpoint).

 

[randy holmes-farley]

Nope, that just about what the alkalinity is in the ocean. Folks that keep higher alkalinity in reef aquaria are not matching the ocean:

http://www.advancedaquarist.com/issues/ ... mistry.htm

 

[randy holmes-farley]

Actually, I guess that I never explicitly showed NSW alkalinity in that article. It is shown in this one:

http://reefkeeping.com/issues/2002-04/r ... /index.htm

 

[Fastmarc]

Thanks for the reply, Randy. Your article is very interesting.
This topic is very interesting. Why is it that the common suggestion is to have the alkalinity at such high levels (3.5 to 4.5 meq/L), most of the time sacrificing the balance that is required between calcium and alkalinity?
I must admit that I was worried about my seemingly low alk levels, but as I do all my water changes with natural sea water and the ph doesn't swing too dramatically (due to a lit refugium), I do not think it necessary to try and improve on nature.
Would you agree?

 

[randy holmes-farley]

I usually recommend 2.5-4 meq/L alkalinity.

There are several reasons to have above NSW alkalinity, all of which are basically sound reasons:

1. Better pH stability because of the buffering of the carbonate/bicarbonate.

2. Faster growth of some calcifying corals.

3. Less liklihood of going below 2.5 meq/L alkalinity before the next addition of alkalinity supplement.

All of the other reasons that I've heard seem marginal as to being correct.

 

[Fastmarc]

Thanks again, Randy

 

[randy holmes-farley]

You're welcome.

 

[delbeek]

Randy I would add a fourth reason for using higher than normal alkalinity:

4) Higher alkalinity allows corals to calcify in high nutrient water such as found in a home aquarium. Marlin Atkinson's students have shown this to be true in work done at Biosphere II.

Aloha!
Charles

 

[randy holmes-farley]

Yes, I agree. The "toxicity" due to nitrate in some corals is eliminated by extra alkalinity. I discuss that in my nitrate article:

http://www.advancedaquarist.com/issues/ ... 3/chem.htm