How to measure Gh in brackish aquarium?

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Daviem

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Hi I used reverse osmosis to setup my brackish aquarium so I needed to increase the GH by adding a product to re mineralise the water, I purchased a API GH tester but it didn’t change no matter how many drops I used then someone said the GH tester doesn’t work with saltwater, is this true ? I have looked and can’t find any product to measure GH in saltwater so I thought try TDS meters but a lot of people say they measure everything in the water so won’t give a real GH reading, so I have no clue how I’m going to monitor the aquariums GH, Any advise how I can test the brackish water GH?
 

Colin_T

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Get a container of reverse osmosis (R/O) water and add mineral salts to get the GH up to whatever you want. Brackish water is usually around 250-350ppm.

After you have increased the GH, add the salt (sodium chloride).

If you are using a marine salt mix, it should state on the packet what the GH will be increased by.

GH test kits should work on sea water but the GH will be quite high so maybe you have very hard water and didn't add enough drops of the test reagent.

TDS (total dissolved solids) meters will measure anything that is in the water including minerals, salts and sediment floating around the water.
 

ChefAlex

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Hi I used reverse osmosis to setup my brackish aquarium so I needed to increase the GH by adding a product to re mineralise the water, I purchased a API GH tester but it didn’t change no matter how many drops I used then someone said the GH tester doesn’t work with saltwater, is this true ? I have looked and can’t find any product to measure GH in saltwater so I thought try TDS meters but a lot of people say they measure everything in the water so won’t give a real GH reading, so I have no clue how I’m going to monitor the aquariums GH, Any advise how I can test the brackish water GH?

Just curious, are you testing general hardness for any specific reason? Importantly, what salinity are you aiming for?

EDIT: Also, I might be misinterpreting, you are using a remineralizing product and a marine salt mix?
 
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Daviem

Daviem

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Hi, I used reverse osmosis water added marine salt to bring the salinity to 1.005 as that’s what the fish require as juveniles, I was then told there would be no GH due to using reverse osmosis water and these fish need between 8-20 GH so I asked and was told to add enough re mineraliser to increase GH by 10 (Seachem replenish) that made the salinity go up to 1.006. I purchased API GH tester clearly states freshwater even after 40 drops won’t change colour tested before and after adding the re mineraliser, then I bought API test strips for fresh and saltwater in the fine print it says GH test doesn’t work in saltwater, so now I’m left not knowing if my GH is very high from the marine salt or actually low still and don’t know if the re mineraliser worked or not. The salt says on the website instant ocean to get proper hardness you need to make the salinity 1.025, I used 1/5th the dose of salt to make it the salinity 1.005. They’re baby Columbian sharks. So need a Gh preferably of 10 minimum but salinity maximum 1.010 at their current size.

Thanks

David
 

ChefAlex

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Hi, I used reverse osmosis water added marine salt to bring the salinity to 1.005 as that’s what the fish require as juveniles, I was then told there would be no GH due to using reverse osmosis water and these fish need between 8-20 GH so I asked and was told to add enough re mineraliser to increase GH by 10 (Seachem replenish) that made the salinity go up to 1.006. I purchased API GH tester clearly states freshwater even after 40 drops won’t change colour tested before and after adding the re mineraliser, then I bought API test strips for fresh and saltwater in the fine print it says GH test doesn’t work in saltwater, so now I’m left not knowing if my GH is very high from the marine salt or actually low still and don’t know if the re mineraliser worked or not. The salt says on the website instant ocean to get proper hardness you need to make the salinity 1.025, I used 1/5th the dose of salt to make it the salinity 1.005. They’re baby Columbian sharks. So need a Gh preferably of 10 minimum but salinity maximum 1.010 at their current size.

Thanks

David
For right now, I would say you are very likely fine. If you measured seachem replenish to raise general hardness to 10GH and then added instant ocean mix theres little chance that you’d be out of range, even if you can’t accurately test right now.

Like Colin_T said next time add your replenish and then test GH with your freshwater test, follow that by adding the amount of instant ocean desired.
 
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Daviem

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Hey, thanks for the help, you don’t think the instant ocean would have made the GH massively high would it the site states it immitates natural sea water at full salinity, but I used 1/5th yes I measured the replenish dose to raise the GH by 10.
 

ChefAlex

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Hey, thanks for the help, you don’t think the instant ocean would have made the GH massively high would it the site states it immitates natural sea water at full salinity, but I used 1/5th yes I measured the replenish dose to raise the GH by 10.
Quite unlikely. Even if your GH was at 20 you would still be fine.
 
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Daviem

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Thank you very much :), I appreciate that now I just need to figure out how to increase the KH without increasing the GH anymore as it’s just 2kh 40 ppm and the PH is dropping.
 

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Thank you very much :), I appreciate that now I just need to figure out how to increase the KH without increasing the GH anymore as it’s just 2kh 40 ppm and the PH is dropping.
That would be a problem. What test kit are you using?
 
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Daviem

Daviem

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That would be a problem. What test kit are you using?
API test kits the master kit and the ph was 7.6-7.8 but it’s dropped to 7 and also for the KH as apparently the KH test kit does work in saltwater, I also have API strips and it showed KH at 40ppm and ph now 7.
 

ChefAlex

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Your gH, alkalinity and pH won’t all be near marine conditions since your salinity is only hovering at 1.005/1.006sg. Natural seawater alkalinity is about 125ppm/7dKh/2.5meqL, so 40ppm sounds about right for your current salinity.

That being said, alkalinity is rather important soley for pH stability. More important than GH. Your pH shouldn’t have swings as large as you’ve stated. I wouldn’t go changing parameters in the tank now, but I would monitor parameters closely. Also note that any test kits designed for freshwater are probably not working accurately at 1.005/6sg. I couldn’t decipher in your last post if that was the case or not.

When you do your first water change you could
add some kalkwasser or sodium bicarbonate to the mix, both are very effective and cheap ways to raise alkalinity. Adding a buffering substrate to the system might help some too. You’re using RO water and adjusting parameters, so sticking to the same method and measurements once you dial in your parameters is crucial. As you increase salinity as the Columbian sharkcats age, you will need to re-evaluate as needed, most likely eschewing anything but the salt mix once you get towards half strength seawater.
 
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Daviem

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Ok thanks for the detailed reply :), I am using freshwater master test kit simply because someone said brackish water is closer to freshwater than saltwater also on YouTube they demonstrated very little difference in those tests being used on both salt and fresh water and vice versa, in the future should I move to saltwater only tests?
Thanks

David
 

ChefAlex

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Ok thanks for the detailed reply :), I am using freshwater master test kit simply because someone said brackish water is closer to freshwater than saltwater also on YouTube they demonstrated very little difference in those tests being used on both salt and fresh water and vice versa, in the future should I move to saltwater only tests?
Thanks

David
That’s a difficult answer and there’s quite a few variables. The titration method is based on a sample of titrates with a known composition (the reagent) interacting with with the analyte (the aquarium water). When the analyte in question deviates slightly from the intended use the reagents are designed to interact with, results will vary. Sometimes it won’t react at all, sometimes wildly or sometimes fairly accurately. The composition of the reagents determines how it will interact, and will vary from test kit to test kit.

In your case, slightly elevated sodium levels might be enough to throw testing accuracy off, but again there is no real way to determine this without employing a known accurate test method side by side with your current method. A salinity of 1.005 is certainly closer to freshwater and a marine test kit would not yield accurate results, keep this in mind as you elevate salinity levels in time. A salinity of 1.010 for example, might be too salty for a freshwater test kit to register at all but not salty enough for accurate marine test numbers.

If you can find testers that can be used in both fresh and saltwater, I would say this would be your best bet by far. Off the top of my head I am unaware of any hobbyist brands that test for both. You may need to delve a little deeper and look into Hanna Instruments, La Motte and the like.
 

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