Ph and carbonate.Hello.I am adding sodium hydroxide NaOH in order to raise ph which is now around 8.3 and I am happy with that.On the other hand the K

Iyad Aoun · Oct 20, 2023

Hello everyone,
It’s been a while I am adding NaOH sodium hydroxide in my 800 litres tank and ph never drops below 8.2 or 8.4 during the day.I am happy with that.On the other hand the KH is always around 9,less happy with it because I have the feeling lower is better but things are fine with my sps and lps.With this relative high value of kh ,I am not adding carbonate Hco3- so my question is : Will this slow down coral growth or I have to change more frequently water ?
Thank you for your suggestions
Iyad Aoun

Timfish · Oct 20, 2023

Main reason I see for consistant water changes is reduce pollutants that can affect corals and that we can't test for and are not removed by skimmers or GAC. As far as KH (alkalinity) I'd say always monitor it along with calcium and magnesium and pH. Things are dynamic in aquaria and while the "big 4" may stay stable for a long time complacency will bite you sooner or later.

Randy Holmes-Farley · Oct 20, 2023

At your pH, there is very, very little hydroxide present and plenty of bicarbonate and carbonate for corals.

The alk from hydroxide is below 0.01 dKH at pH 8.3, no matter what you dosed or did not dose to get there.

Iyad Aoun · Oct 20, 2023

Randy Holmes-Farley said:
At your pH, there is very, very little hydroxide present and plenty of bicarbonate and carbonate for corals.

The alk from hydroxide is below 0.01 dKH at pH 8.3, no matter what you dosed or did not dose to get there.

Hello again,so if I understand Naoh is not the cause of high kh values,thing is that since I am adding naoh ,kh values are around 9 v/s 7 before adding naoh.I will cknsult the link you sent,correct me if I am wrong.Thank you

Randy Holmes-Farley · Oct 20, 2023

Iyad Aoun said:
Hello again,so if I understand Naoh is not the cause of high kh values,thing is that since I am adding naoh ,kh values are around 9 v/s 7 before adding naoh.I will cknsult the link you sent,correct me if I am wrong.Thank you

Adding sodium hydroxide boosts alkalinity. It is a high pH alkalinity supplement, and we have a variety of DIY recipes and calculators for using it in that way.

Here's an adaptation of a section of one of my articles:

The sodium ions in the solution obviously supply sodium to the aquarium (which is mostly not important), and the hydroxide ions supply alkalinity. Hydroxide itself provides alkalinity (both by definition and as measured with an alkalinity test), but corals consume alkalinity as bicarbonate, not hydroxide. Fortunately, when hydroxide is used in a reef aquarium, it quickly combines with atmospheric and dissolved carbon dioxide and bicarbonate to form bicarbonate and carbonate:

4. OH- + CO2 --> HCO3-

5. OH- + HCO3- --> CO3-- + H2O

In an aquarium with an acceptable pH, there is no concern that the alkalinity provided is any different from any other carbonate alkalinity supplement. The hydroxide immediately disappears into the bicarbonate/carbonate system. In other words, the amount of hydroxide present in aquarium water is really a function of only pH (regardless of what has been added), and at any pH below 9, it is an insignificant factor in alkalinity tests (much less than 0.1 meq/L). Consequently, the fact that alkalinity is initially supplied as hydroxide is not to be viewed as problematic, except as it impacts pH.

Iyad Aoun · Oct 20, 2023

Randy Holmes-Farley said:
Adding sodium hydroxide boosts alkalinity. It is a high pH alkalinity supplement, and we have a variety of DIY recipes and calculators for using it in that way.

Here's an adaptation of a section of one of my articles:

The sodium ions in the solution obviously supply sodium to the aquarium (which is mostly not important), and the hydroxide ions supply alkalinity. Hydroxide itself provides alkalinity (both by definition and as measured with an alkalinity test), but corals consume alkalinity as bicarbonate, not hydroxide. Fortunately, when hydroxide is used in a reef aquarium, it quickly combines with atmospheric and dissolved carbon dioxide and bicarbonate to form bicarbonate and carbonate:

4. OH- + CO2 --> HCO3-

5. OH- + HCO3- --> CO3-- + H2O

In an aquarium with an acceptable pH, there is no concern that the alkalinity provided is any different from any other carbonate alkalinity supplement. The hydroxide immediately disappears into the bicarbonate/carbonate system. In other words, the amount of hydroxide present in aquarium water is really a function of only pH (regardless of what has been added), and at any pH below 9, it is an insignificant factor in alkalinity tests (much less than 0.1 meq/L). Consequently, the fact that alkalinity is initially supplied as hydroxide is not to be viewed as problematic, except as it impacts pH.

Super,clear to me now.So i will stop adding hco3 and continue using naoh...thank you