Low dKH in fresh saltwater mix. Looking for reasons.

[EricHL]

Hi Reefers


I am new in reefing and I have a quick (and probably very stupid) question. Can I make mistakes in storing slat, which influences the dKH I can achieve with the salt?

Background: I had trouble with my dKH levels (I am using the Hanna checker to test dKH). Those problems are strange since I do not have any skeleton building corals … anymore. Just softies and anemones (Zoas, Ricordeas, etc.). I tried to correct the low dKH with dosing tropic marin all for reef.

Today I checked the dKH after a water change. It was much lower than before the waterchange. So I made a new saltwater mix (Colombo Pro Reef Salt) to test its dKH. The dKH of the fresh saltwater mix was at 5.9! The label on the bag tells me that I can expect a dKH of 9 at a salinity of 35ppt (1.026). The calibration of my refractometer has been checked.

Now I am interested in finding the reason for this difference. May I have just been unlucky with this specific bag of salt or may I have made any mistake?

Do you have any I idea what I may have done wrong?



Thank you and best regards

Eric

 

[Garf]

Hi Reefers


I am new in reefing and I have a quick (and probably very stupid) question. Can I make mistakes in storing slat, which influences the dKH I can achieve with the salt?

Background: I had trouble with my dKH levels (I am using the Hanna checker to test dKH). Those problems are strange since I do not have any skeleton building corals … anymore. Just softies and anemones (Zoas, Ricordeas, etc.). I tried to correct the low dKH with dosing tropic marin all for reef.

Today I checked the dKH after a water change. It was much lower than before the waterchange. So I made a new saltwater mix (Colombo Pro Reef Salt) to test its dKH. The dKH of the fresh saltwater mix was at 5.9! The label on the bag tells me that I can expect a dKH of 9 at a salinity of 35ppt (1.026). The calibration of my refractometer has been checked.

Now I am interested in finding the reason for this difference. May I have just been unlucky with this specific bag of salt or may I have made any mistake?

Do you have any I idea what I may have done wrong?



Thank you and best regards

Eric

First would be to double check the salinity. If you calibrated with RO water, that could be significant.

 

[EricHL]

First would be to double check the salinity. If you calibrated with RO water, that could be significant.

Thank you.
Yes I have calibrated with RO water. Which alternative calibration or measurement technique can you suggest? (Electric salinity probe?)

 

[Garf]

Thank you.
Yes I have calibrated with RO water. Which alternative calibration or measurement technique can you suggest? (Electric salinity probe?)

I make my own, thanks to Randy Holmes-Farley;

http://reefkeeping.com/issues/2006-12/rhf/#18

 

[N.Sreefer]

"All corals have skeletons made of calcium carbonate, the same material that composes shells. This diagram shows the various forms of coral skeletons. Tropical reef corals secrete their skeletal material in the form of cups that hold each polyp. As the colony grows, more calcium carbonate is secreted below the polyp. In soft corals and gorgonians, the calcium carbonate occurs in the form of small needles, “flowers”, “dumbbells”, or plates, all with the general name sclerite. The sclerites are usually embedded in the outer layer of tissue around the polyp but can also be found throughout the colony. They may be arranged in a variety of ways, a typical one being in the shape of a V-shaped bar. In some groups, the sclerites occur as plates on the outside of the colony, forming protective cups around the polyps. No matter what the shape or arrangment, most are truly beautiful and intricate structures."

Taken from https://oceanexplorer.noaa.gov/explorations/03mountains/background/octocorals/media/sclerite.html

All coral sequester calcium carbonate to some degree.

 

[EricHL]

"All corals have skeletons made of calcium carbonate, the same material that composes shells. This diagram shows the various forms of coral skeletons. Tropical reef corals secrete their skeletal material in the form of cups that hold each polyp. As the colony grows, more calcium carbonate is secreted below the polyp. In soft corals and gorgonians, the calcium carbonate occurs in the form of small needles, “flowers”, “dumbbells”, or plates, all with the general name sclerite. The sclerites are usually embedded in the outer layer of tissue around the polyp but can also be found throughout the colony. They may be arranged in a variety of ways, a typical one being in the shape of a V-shaped bar. In some groups, the sclerites occur as plates on the outside of the colony, forming protective cups around the polyps. No matter what the shape or arrangment, most are truly beautiful and intricate structures."

Taken from https://oceanexplorer.noaa.gov/explorations/03mountains/background/octocorals/media/sclerite.html

All coral sequester calcium carbonate to some degree.

Hello Sreefer.
Ah ok. So I was wrong with my assumption that my softies do not influence the dKH at all.

Thank you

Nevertheless, I still need to check the calibration of my refectometer.

Have a nice weekend.
Eric

 

[Shirak]

You could try mixing some salt mix by volume instead of using the refractometer. I think it's slightly over half cup/Gal Something like that. Would have to look into it further. Although it's highly likely the refractometer and not mixing to 35ppt, it might be worth mixing your dry salt before using. There have been reports of settling, which could give inconsistent results when mixing with water. I use HW Marinemix Reef which comes vacuum packed so it's not going to settle during transport but I mix it anyway when I open a new box. Plastic buckets are more prone if the salt is loose inside. Take the bucket and put the lid on securely and roll it around/shake it for a bit.

 

[EricHL]

Update: Numbers corrected. THX to Graf.
Thank you everybody for your support. Here is a short update. First I have recalibrated the refractometer. Just to be very sure.

I have read the link Graf gave me. In the description it is recommended that the calibration should be done with 2 solutions RO water and a known solution.
So I have made fresh salt water. To achieve 30ppt I should need 1000g of salt for 30l of water.

So I took 33g for 1l and mixed it up well.

Now we got… drumroll please… a salinity of close to 30ppt (1.022 specific gravity).

Now I wanted to have a reference measurement. I went to the LFS and bought the only device they had available. A floating salimeter. I put it into the water and got a very similar value around 1.020 specific gravity.

Then I found my mistake. The temperature in the water was only 20°C.

In the refractometer images above you can see that it expects a temperature of 25°C. MY room-temperature is below 25°C. Thus, it will not heat up in the refractometer. This induces an systematic error which depends on the temperature difference. After looking up the dependency of spcific gravity temperature and salinity, I have found that my real salinity was anywhere around 27.2ppt.

I still need to find out if this is the final answer. But think I am a lot closer to it.

Thanks angain for all the good advice. You all hepled me a lot.

Best Regards
Eric

 

[Garf]

Thank you everybody for your support. Here is a short update. First I have recalibrated the refractometer. Just to be very sure.

I have read the link Graf gave me. In the description it is recommended that the calibration should be done with 2 solutions RO water and a known solution.
So I have made fresh salt water. To achieve 35ppt I should need 1000g of salt for 30l of water.

So I took 33g for 1l and mixed it up well.

Now we got… drumroll please… a salinity of close to 30ppt (1.022 specific gravity). 5ppt less than intended.

Now I wanted to have a reference measurement. I went to the LFS and bought the only device they had available. A floating salimeter. I put it into the water and got a very similar value around 1.020 specific gravity.

Then I found my mistake. The temperature in the water was only 20°C.

In the refractometer images above you can see that it expects a temperature of 25°C. MY room-temperature is below 25°C. Thus, it will not heat up in the refractometer. This induces an systematic error which depends on the temperature difference. After looking up the dependency of spcific gravity temperature and salinity, I have found that my real salinity was anywhere around 27.2ppt to 30ppt. That explains quite a bit.

I still need to find out if this is the final answer. But think I am a lot closer to it.

Thanks angain for all the good advice. You all hepled me a lot.

Best Regards
Eric

Ok. To get 35ppt you would need at least 35grammes per liter, however because the salt has a water content it would probably more like 37 or 38grammes to make a 35ppt standard.

 

[EricHL]

Hello Reefers

I made further progress with the issue. I have increased the Salinity of the solution two times. Due to the findings mentioned above, I have controlled the temperature.

1st increase to 35ppt measured with the refractometer (temperature control difficult).
2nd increase to 35ppt measured with the floating salometer (temperaure control easy).

For both solutions I have measured the alkalinity with the Hanna checker and with the ReadSea test kit.

In both solutions both alkalinity tests agreed, that the alkalinity was ridiculously low (sometimes even in the range of 4.9 and 5). (The exact point was very difficult to see with the red sea reefer test kit.)

Since both measurement techniques agree, I believe something must be seriously wrong with the water or with the salt or with the buckets/glases I use. The tap water in my city is very high in alkalinity (12,04 dKH). So, I believe that my RO system is still working fine.

Now I am back to my original assumption that there is something wrong with the salt. I have ordered a new bucket of slat. It will arrive on Wednesday. I will keep you updated whether changing the salt solves my problem.



Best Regards

Eric

 

[attiland]

Hello Reefers

I made further progress with the issue. I have increased the Salinity of the solution two times. Due to the findings mentioned above, I have controlled the temperature.

1st increase to 35ppt measured with the refractometer (temperature control difficult).
2nd increase to 35ppt measured with the floating salometer (temperaure control easy).

For both solutions I have measured the alkalinity with the Hanna checker and with the ReadSea test kit.

In both solutions both alkalinity tests agreed, that the alkalinity was ridiculously low (sometimes even in the range of 4.9 and 5). (The exact point was very difficult to see with the red sea reefer test kit.)

Since both measurement techniques agree, I believe something must be seriously wrong with the water or with the salt or with the buckets/glases I use. The tap water in my city is very high in alkalinity (12,04 dKH). So, I believe that my RO system is still working fine.

Now I am back to my original assumption that there is something wrong with the salt. I have ordered a new bucket of slat. It will arrive on Wednesday. I will keep you updated whether changing the salt solves my problem.



Best Regards

Eric

Some salt known to have levels different in almost every batch. Instant Ocean is mentioned in those conversations a lot. I don’t know your salt but this could be the case.
two things to whatch out for is temperature (you already figured that one out) and calibration of refractometer. Latter could be calibrated to 35ppt reference fluid if you want good reading. You can pick up these for £5 on eBay and gas about 50-10ml in there. Enough for years. Your own reference fluid will not be good enough.

 

[Shirak]

Did you order the same salt or are you trying a different brand? Have you tried mixing the dry salt in case it has settled during shipping? If the bucket says it should be 9dkh and you are reading 5 that is a pretty big difference.

Have you tried testing Calcium in your tank and also the fresh mixed SW? Does the salt bucket indicate what those levels should be after mixing? If so and your testing the proper amount then it could be a problem with the alk in the mix.

 

[EricHL]

Did you order the same salt or are you trying a different brand? Have you tried mixing the dry salt in case it has settled during shipping? If the bucket says it should be 9dkh and you are reading 5 that is a pretty big difference.

Have you tried testing Calcium in your tank and also the fresh mixed SW? Does the salt bucket indicate what those levels should be after mixing? If so and your testing the proper amount then it could be a problem with the alk in the mix.

Hello Shirak
Thank you for the reply.

I am trying out a new brand (read sea coral pro).
Have I tried mixing the dry slat in the case it has been settled? I am not quite sure what you refering to here. Can you explain? I mixed the salt with RO water. I let it stand still for some hours with a heater in the bucket (25°C) untill almost everything is resolved (it does not resolve completely, no matter how long I wait).

The calium seems to be fine (451 measured with Hanna Checker). The label says it should be at 420.

Best Regards
Eric

 

[Shirak]

Hello Shirak
Thank you for the reply.

I am trying out a new brand (read sea coral pro).
Have I tried mixing the dry slat in the case it has been settled? I am not quite sure what you refering to here. Can you explain? I mixed the salt with RO water. I let it stand still for some hours with a heater in the bucket (25°C) untill almost everything is resolved (it does not resolve completely, no matter how long I wait).

The calium seems to be fine (451 measured with Hanna Checker). The label says it should be at 420.

Best Regards
Eric

Hi Eric,
There have been cases of the dry salt settling and separating in the container during shipping. The finer particles move to the bottom and the dry salt is no longer uniform throughout the bucket. The dry salt should be mixed well prior to using so it's more homogenous throughout. It could explain some differences from the manufacturer numbers if only taking a small amount out off the top of the bucket. Of course the other explanation is the manufacturer quality control in producing a product which matches what they claim. Red Sea Coral Pro is good. Careful about changing the tank over too fast. The new salt will have a pretty high Alk. compared to where you are currently.

BRS video on salt stratification

 

[FoolintheRain]

Hello Shirak
Thank you for the reply.

I am trying out a new brand (read sea coral pro).
Have I tried mixing the dry slat in the case it has been settled? I am not quite sure what you refering to here. Can you explain? I mixed the salt with RO water. I let it stand still for some hours with a heater in the bucket (25°C) untill almost everything is resolved (it does not resolve completely, no matter how long I wait).

The calium seems to be fine (451 measured with Hanna Checker). The label says it should be at 420.

Best Regards
Eric

Do you have your heater turned on while you are adding the salt mix? I had a similar problem and realized that when I left the heater on while I added the salt it created a lot of precipitation. Once I started getting the RODI water up to temperature (Fritz recommends 72-75 F) and turning off the heater before adding the salt and letting it mix for 30 minutes or so before turning the heater back on, there was no more precipitate and the levels measured to what they were supposed to be. Even though your heater is set to 25 degrees, the water right next to the heater will be much warmer than that, especially without a lot of circulation.

 

[EricHL]

Hi Eric,
There have been cases of the dry salt settling and separating in the container during shipping. The finer particles move to the bottom and the dry salt is no longer uniform throughout the bucket. The dry salt should be mixed well prior to using so it's more homogenous throughout. It could explain some differences from the manufacturer numbers if only taking a small amount out off the top of the bucket. Of course the other explanation is the manufacturer quality control in producing a product which matches what they claim. Red Sea Coral Pro is good. Careful about changing the tank over too fast. The new salt will have a pretty high Alk. compared to where you are currently.

BRS video on salt stratification

Thank you for the video. I did not know this effect.
I mixed the dry slat and tested again. No difference. the dKH was very low (around 5).

Today the new salt arrived (RedSea Coral Pro).
I just run the same test with the new salt. The dKH was 11.6 (the label says 12). Almost perfect match.

I have no idea what may have caused the low dKH in the old salt. I could swear that, at the beginning, the old salt also raised the dKH to levels around 8 after a water change. I think that I have done something wrong with the way I have stored the salt. I dont know what it may be. May be the humidity (I have no humidity sensor so I can just guess).

Anyway. I have an eye on the new salt so I can detect any drop in dKH.

Thanks again to everybody.
Best Regards
Eric