Natural Salt Water Parameters

fishybizzness

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So just in case anyone is interested. I live in the Caribbean and collect nsw for most of my water changes. I collect it off of a beach down the hill from my house where I go snorkeling. There are several types of entrusting as well as branching coral growing about 20 feet off the beach from where I collect. Not full blown reefs but more scattered smaller pieces due to the beach being a very popular swimming and boating area. I collect on the incoming tide usually on weekday afternoons due to the boating traffic being mostly on the weekends. I've been doing this for several years and haven't really had any issues from this practice that I know of. The only adjustment I make is to the alkalinity because I like to run my tanks at around 8 dkh. I tested the water that I collected this weekend just out of curiosity and the parameters are as follows:

Salinity- 1.026 - Millwaukee refractometer.
Nitrate- Undetectable-Red Sea
Calcium- 400- Red Sea
Magnesium- 1440-1450- Red Sea
Alkalinity- 7.3- Hannah
Phosphate-.02- Hannah.
This is where I collect. 20201121_083602.jpg
 

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ReefRusty

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I too also use NSW however i know the alk is 7.5 and salinity is a high 1.028, phos 0.01 unsure on calcium and mag

This is collected 100m of shore of a rock wall. Minimal boating around the area that is collected from.
 

Randy Holmes-Farley

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Interesting on the nitrate.

Nitrate in the ocean near the surface is typically less than 1 ppm, and often below 0.1 ppm unless the water is polluted.

Hence the old mantra of trying to keep nitrate undetectable.

But in a reef tank lacking the natural foods of the ocean, that causes problems.
 

Randy Holmes-Farley

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So just in case anyone is interested. I live in the Caribbean and collect nsw for most of my water changes. I collect it off of a beach down the hill from my house where I go snorkeling. There are several types of entrusting as well as branching coral growing about 20 feet off the beach from where I collect. Not full blown reefs but more scattered smaller pieces due to the beach being a very popular swimming and boating area. I collect on the incoming tide usually on weekday afternoons due to the boating traffic being mostly on the weekends. I've been doing this for several years and haven't really had any issues from this practice that I know of. The only adjustment I make is to the alkalinity because I like to run my tanks at around 8 dkh. I tested the water that I collected this weekend just out of curiosity and the parameters are as follows:

Salinity- 1.026 - Millwaukee refractometer.
Nitrate- Undetectable-Red Sea
Calcium- 400- Red Sea
Magnesium- 1440-1450- Red Sea
Alkalinity- 7.3- Hannah
Phosphate-.02- Hannah.
This is where I collect. 20201121_083602.jpg

FWIW, there is likely some problem with the numbers, since you are not near a substantial river input that might be messing with the ratios.

The ratio of calcium to magnesium to alk does not vary enough in the ocean to allow that combination, regardless of the salinity. It is very well established how much of the major ions are present in seawater at a given salinity, and it does not vary as much as you report.

Most likely, the magnesium is not accurate, as is apparently fairly common with the Red Sea kit for some reason.

The ratio (shown at at 35 ppt) is:

~1280 ppm magnesium
~420 ppm calcium
~6.5 dKH alkalinity
 
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fishybizzness

fishybizzness

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FWIW, there is likely some problem with the numbers, since you are not near a substantial river input that might be messing with the ratios.

The ratio of calcium to magnesium to alk does not vary enough in the ocean to allow that combination, regardless of the salinity. It is very well established how much of the major ions are present in seawater at a given salinity, and it does not vary as much as you report.

Most likely, the magnesium is not accurate, as is apparently fairly common with the Red Sea kit for some reason.

The ratio (shown at at 35 ppt) is:

~1280 ppm magnesium
~420 ppm calcium
~6.5 dKH alkalinitY
That is a good point with the magnesium as i have always found my tank water to be a little high when testing. Are there any test kits that you recommend for testing magnesium?
 

Randy Holmes-Farley

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I actually don't think most people need to measure it, if they use a calcium and alk additive system that includes it.

Many folks seem to think the Salifert magnesium kit is good, but be sure to not read the syringe backward.
 
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