Instant ocean dGH using reverse osmosis water

daviem

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Hi, does anyone know what the GH of instant ocean is after being added to reverse osmosis water at full salinity aka 1.026 so I can try and figure out what my aquarium water GH is.

thanks

David.
 
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You don't really need to measure GH as it is irrelevant in the reef tank. It is the KH which matters.
 
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daviem

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The fish I have currently are brackish as juveniles then move up to full saltwater as adults loads of places mention their GH requirements so I want to figure out the GH of the water after adding IO as there’s no GH test kits for saltwater I figured if someone knew the standard IO GH I could calculate it that way. Also as I’m using a lower salinity of instant ocean with reverse osmosis water I’m wondering if there’s enough GH or any risk of osmotic shock.
 
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Randy Holmes-Farley

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The fish I have currently are brackish as juveniles then move up to full saltwater as adults loads of places mention their GH requirements so I want to figure out the GH of the water after adding IO as there’s no GH test kits for saltwater I figured if someone knew the standard IO GH I could calculate it that way. Also as I’m using a lower salinity of instant ocean with reverse osmosis water I’m wondering if there’s enough GH or any risk of osmotic shock.

Osmotic shock is unrelated to GH in seawater.

Any freshwater GH kit will accurately give GH in seawater, but it will be very high.

GH in seawater is a strange mix of calcium and magnesium. All mixes have enough GH for any organism. As I show below, full strength seawater is about 6,300 ppm GH. At a sg of 1.013 (half strength seawater) you will still have more than 3,000 ppm GH.

Osmotic properties are mostly driven by sodium and chloride since they are in far higher concentration than calcium and magnesium.


GH (general hardness)

Hardness is a characteristic of water due to the presence of dissolved calcium and magnesium. Water hardness is responsible for most scale formation in pipes and water heaters (calcium and magnesium carbonates, typically), and forms insoluble solids when it reacts with soaps. Hardness is often expressed in grains per gallon, parts per million or milligrams per liter, all as calcium carbonate equivalents. It is a measure often used in freshwater aquarium systems, but not often in marine systems, where its values are very large.Seawater has a total (general) hardness of about 6.3 g/L (6,300 ppm) of calcium carbonate equivalents.These linked articles detail aspects of magnesium and calcium in seawater.
 
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daviem

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Hi thanks for the helpful response, it helps me along the way to try and figure out if the GH is enough for them, they’re currently at a salinity of 1.005-1.006, I’m thinking of increasing that to 1.007 so that’s the concentration of 1/4 seawater, they’re still very small so I’m not sure if that’s too early.

Your response suggested what I believed that I should not have used products to increase the GH even further after adding instant ocean but many on other forums and some manufacturers encouraged me to do so despite knowing I used instant ocean stating the water had no GH because I used reverse osmosis water and they would die of osmotic shock. 1 manufacturer ntlabs stated differently that I shouldn’t be adding more minerals.

I now know how to calculate the GH in the water by only counting the minerals so would you agree basically if the minerals aka magnesium and calcium and potassium in the salinity of the aquarium are already creating higher GH than they recommend for this fish I should not be increasing the GH with products such as Seachem Replenish and there’s no risk of osmotic stress using Instant ocean and reverse osmosis water? I know I still need to keep an eye on the water KH separately.

thanks again
 

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