Why Is Alk Rising?

[aidensav]

test the alk right after your mix.

also, check your ato system. make sure it is working correctly.

Ato is working well, tested the mix at 8.4 dkh

 

[Randy Holmes-Farley Verified Community Expert]

I'd just keep monitoring, and drop it as I suggested if it keeps going up.

 

[aidensav]

I'd just keep monitoring, and drop it as I suggested if it keeps going up.

Ok, thanks for the help

 

[aidensav]

Update: I added 15 grams of muriatic acid to 11 gallons of freshly made saltwater. Today, I changed half a gallon of the tank water with the 0 alk water. It dropped the ph down to 7.4 and the alkalinity is now around 8.5. Corals are not too happy.

Did I do something wrong? I put the new water in slowly and in a “high flow” area.

 

[aidensav]

I tested 3 days ago and it said it was 10.9 dkh as well

 

[Randy Holmes-Farley Verified Community Expert]

Update: I added 15 grams of muriatic acid to 11 gallons of freshly made saltwater. Today, I changed half a gallon of the tank water with the 0 alk water. It dropped the ph down to 7.4 and the alkalinity is now around 8.5. Corals are not too happy.

Did I do something wrong? I put the new water in slowly and in a “high flow” area.

You may have added a bit too much muriatic acid to the new salt water to see that large of an alk drop in the tank.

You should aerate the new water a lot to drive off CO2 before adding it. You should be able to bring to the pH to 7 or above.

Here’s a copy and paste of my recipe:

You can use muriatic acid or certain freshwater buffers to lower alk.
Both will lower pH similarly and a lot. There's no way around the pH lowering when reducing alkalinity. You do not want to add CO2. You want to remove CO2 from the tank via aeration.

For that reason, it is best to do it in water change water that is aerated to raise pH before using, or to do it very slowly in the tank (over many days).

The "acidity" (that being essentially negative alkalinity) of muriatic acid straight from the bottle is about 11,000 meq/L.

So adding 1/11,000 of the water volume as this acid will drop alkalinity by 1 meq/l (2.8 dKH).

I would not drop more than 1 dKH per day due to the big pH drop in a reef tank, but in new salt water it is fine.

You'll need to aerate well after adding the acid to blow off the excess CO2 and bring up the pH.

 

[aidensav]

Update: I added 15 grams of muriatic acid to 11 gallons of freshly made saltwater. Today, I changed half a gallon of the tank water with the 0 alk water. It dropped the ph down to 7.4 and the alkalinity is now around 8.5. Corals are not too happy.

Did I do something wrong? I put the new water in slowly and in a “high flow” area.

You may have added a bit too much muriatic acid to the new salt water to see that large of an alk drop in the tank.

You should aerate the new water a lot to drive off CO2 before adding it. You should be able to bring to the pH to 7 or above.

Here’s a copy and paste of my recipe:

You can use muriatic acid or certain freshwater buffers to lower alk.
Both will lower pH similarly and a lot. There's no way around the pH lowering when reducing alkalinity. You do not want to add CO2. You want to remove CO2 from the tank via aeration.

For that reason, it is best to do it in water change water that is aerated to raise pH before using, or to do it very slowly in the tank (over many days).

The "acidity" (that being essentially negative alkalinity) of muriatic acid straight from the bottle is about 11,000 meq/L.

So adding 1/11,000 of the water volume as this acid will drop alkalinity by 1 meq/l (2.8 dKH).

I would not drop more than 1 dKH per day due to the big pH drop in a reef tank, but in new salt water it is fine.

You'll need to aerate well after adding the acid to blow off the excess CO2 and bring up the pH.

But how could my 33g tank drop from probably 11.5 dkh to 8 with just 1/2 gal water change?

 

[Randy Holmes-Farley Verified Community Expert]

But how could my 33g tank drop from probably 11.5 dkh to 8 with just 1/2 gal water change?

Too much acid. Maybe more than prescribed?

 

[aidensav]

But how could my 33g tank drop from probably 11.5 dkh to 8 with just 1/2 gal water change?

Too much acid. Maybe more than prescribed?

If this math is correct (from AI), assuming that the original dkh was 12:

12 • 32.5/33 = 11.82 dkh

Can alkalinity be negative?

My math:

0.5/33=0.0152
0.0152•12=0.18

I tested the alk in the new water but the test kit only goes as far as 0 dkh.

 

[Randy Holmes-Farley Verified Community Expert]

If this math is correct (from AI), assuming that the original dkh was 12:

12 • 32.5/33 = 11.82 dkh

Can alkalinity be negative?

My math:

0.5/33=0.0152
0.0152•12=0.18

I tested the alk in the new water but the test kit only goes as far as 0 dkh.

Yes, acid has negative alkalinity. Straight muriatic acid has about -31,000 dKH.

 

[EricR]

I was using Sodium Bisulfate like link in post #19 to fight off increasing alkalinity for more than a year.
I always used air pump and air stone to aerate the newly-mixed low/no alk water overnight to bring up pH before using.

Overnight aeration always got low/no alk water up to pH at least 7 and that had no measurable effect on my tank pH after water change.
*I was mostly doing 3 gallon water changes with around 0.2-0.4 dKH water in 40 gallon tank

 

[Bear22]

CaribSea dry rock is produced from previous reef live rock and it's that denser form of live rock. Half of my display scape is CaribSea dry rock. I do about a 12% WC weekly it lowers my alkalinity each time (using TM's Pro salt). Are you dosing peroxide by chance? That will raise alk for sure.

 

[Privateye]

It sounds like pH shock. The pH will return to normal fairly quickly depending on your level of aeration, but it's best to avoid this if possible.

There are a couple of ways I approach this, and I have to dose muriatic acid in systems with animals fairly often. The first would be to do what you did, but measure the alkalinity and pH in the bucket. If your pH is at a normal level (or close to it - I imagine 7.8 would be fine) then it is safe to use. The alkalinity doesn't need to be 0 in the bucket either, just substantially lower to lower your alkalinity. Closer to 0 would drop it faster though.

The other thing I do is set up a reservoir (let's say a bucket) to dose continuously. I have a very small trickle of water in and out of the bucket (effluent goes back to the system) and I add an air stone to the bucket. I add muriatic acid directly in the bucket once I have the air and water flow rates set. So it's aerating (which helps the pH rise faster) and also exchanging a very small amount of the volume at all times. I have the water from the bucket go into the sump, or another chamber that doesn't contain the animals itself. That way the acid water has more of a chance to mix before it hits the animals.

I once overdosed muriatic in 400 gallons of water (just a reservoir - no animals) and when I went to check the alkalinity the next day, the salifert test turned red as soon as I added the indicator, meaning my pH was 4.5 or below. Not safe! A little baking soda fixed it quickly though.

I have had no losses from acid dosing, and I've been doing it for years. Hope this helps!

 

[Randy Holmes-Farley Verified Community Expert]

Are you dosing peroxide by chance? That will raise alk for sure.

What sort of peroxide are you referring to?

 

[Bear22]

What sort of peroxide are you referring to?

H2O2

 

[aidensav]

I was using Sodium Bisulfate like link in post #19 to fight off increasing alkalinity for more than a year.
I always used air pump and air stone to aerate the newly-mixed low/no alk water overnight to bring up pH before using.

Overnight aeration always got low/no alk water up to pH at least 7 and that had no measurable effect on my tank pH after water change.
*I was mostly doing 3 gallon water changes with around 0.2-0.4 dKH water in 40 gallon tank

did you have a lid on the low alk water?

 

[aidensav]

CaribSea dry rock is produced from previous reef live rock and it's that denser form of live rock. Half of my display scape is CaribSea dry rock. I do about a 12% WC weekly it lowers my alkalinity each time (using TM's Pro salt). Are you dosing peroxide by chance? That will raise alk for sure.

No peroxide

 

[EricR]

did you have a lid on the low alk water?

Loose, just to control evaporation somewhat (i.e. water collecting on bottom of lid) but still allow the pumped in air to escape freely.