Alkalinity in a Reef tank

[Randy Holmes-Farley]

Dear Dr. Randy,

When we talk about alkalinity in a reef tank, is it Alkalinity (M), Alkalinity (P) or Alkalinity (Total)?

Best,
Rabih

With a few exceptions, we are measuring and talking about total alkalinity. In normal seawater, carbonate alkalinity and total alkalinity are quite close, with the small amount of borate alkalinity making up the reminder.

This article has more detail:
http://www.advancedaquarist.com/2002/2/chemistry

 

[drernesto]

With a few exceptions, we are measuring and talking about total alkalinity. In normal seawater, carbonate alkalinity and total alkalinity are quite close, with the small amount of borate alkalinity making up the reminder.

This article has more detail:
http://www.advancedaquarist.com/2002/2/chemistry

Thanks a lot Super amazing Dr.!

 

[Randy Holmes-Farley]

You're welcome and thanks!

Happy Reefing.

 

[Griff]

I've read several of your write ups on alkalinity calcium mag and phosphate. I'm dealing with two issues right now. One has been a continuous issue the other is more recent.

Current parameters as of last water test.
dkh 6.7
Calcium 425
MG 1350
PO4 .35
Nitrate 0


Tank is IM 30l
About 25 coral only 3 Sps


I've been chasing Alk of 9 for what feels like a year probably more like 6-9 months though. I lose approx 1 dkh per day and have to dose about 14 ml of Alk per day. My calcium doesn't seem to move unless I do a water change. Water changes have been more frequently lately approx 2 per week 5 gallons at a time. Trying to get p04 down from a loss of a fish and lack of cleaning sandbed. I'm just not understanding why Alk drops so fast and calcium doesn't move.

My 2 part Alk has crystallized clumps in it but I've tested after dosing and it does seem to raise the Alk as expected. Any help would be appreciated.

The PO4 issue I think I know why I have as stated before. It was as high as .67 a week ago and I've brought it down to the .35 by doing water changes using phosguard in a bag and phosphate sponges. I'll continue this till I get around .03. I have a slight hair algae issue but in my opinion it's not that bad. I'm transferring all corals and live stock to a reefer 525xl once the parameters in that tank are stable and correct. I expect that to take 1-3 months.

Any advice on these two issues would be a huge help.

 

[Griff]

Phosphate checker is Hanna low range
Alk calc and mg Red Sea pro
Nitrate api

 

[drernesto]

Usually when I add GFO (Rowa Phos) my Alk drops a little bit... Maybe phosguard and phosphate sponges have the same effects on Kh
Dr. @Randy might help you more with this.

 

[Griff]

True but it's been an issue since before I was using those products. At least that's how I'm remembering it.

 

[Griff]

Anyone else have any thoughts

 

[serkel]

I would also like to hear the reason to this. I have realized it yet but i will look for this the next time I change my ROWA

 

[Griff]

Bump

 

[Randy Holmes-Farley]

GFO releases iron, and iron is known to catalyze the precipitation of calcium carbonate. That is why, I believe, that GFO gets accumulations of calcium carbonate on them, and become clumped. That also uses up some calcium and alkalinity.

Second, reduced phosphate may increase calcification by corals and maybe even abiotic precipitation of calcium carbonate.

Hence, adding GFO can increase the demand for calcium and alkalinity, and such increases are always seen in alk first since it changes much faster than calcium when over or under dosing (that is because there is a much bigger reservoir of calcium in seawater than alkalinity).

When you are seeing alk change and not calcium, that is just the match of consumption. It always changes a lot more on a percentage basis.

 

[Griff]

great response to the question of using gfo and its affect on alkalinity. But the question of demand for alkalinity in a small tank with very little Sps is still driving me crazy. I've been trying to obtain 9dkh and 425 calc.

My method for achieving this was to raise dkh by 1 per day until I hit 9dkh wait one week test both Alk and calc. And dose accordingly to keep it there. When I retest Alk is always way down around 6.7-7.3 calc is steady between 400-425. Should my Alk be moving that much in relation to the calcium?

If I dose 15 ml of Alk daily it will hold but I don't dose any calcium and it seems to hold steady. This isn't making since to me.

 

[Randy Holmes-Farley]

great response to the question of using gfo and its affect on alkalinity. But the question of demand for alkalinity in a small tank with very little Sps is still driving me crazy. I've been trying to obtain 9dkh and 425 calc.

My method for achieving this was to raise dkh by 1 per day until I hit 9dkh wait one week test both Alk and calc. And dose accordingly to keep it there. When I retest Alk is always way down around 6.7-7.3 calc is steady between 400-425. Should my Alk be moving that much in relation to the calcium?

If I dose 15 ml of Alk daily it will hold but I don't dose any calcium and it seems to hold steady. This isn't making since to me.

Even a soft coral tank can drop 2+ dKH per day.

When you underdose both alk and calcium equally, a drop of 1 dKH will only be accompanied by a drop in calcium of about 6 ppm, which most kits won't see.

But if it is really imbalanced demand, water changes with a mix not matching the tank is by far the most common explanation. Rising nitrate will also cause alk to drop and not calcium.

I discuss such issues here:

When Do Calcium and Alkalinity Demand Not Exactly Balance? by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2004-12/rhf/index.htm

 

[Griff]

Thanks. I've read that article many times. I think it's a bit over my head. Is it ok to just dose the Alk then, while keeping an eye on calc

 

[Griff]

Sorry last comment sounded ungrateful not my intention. That article is the only thing that's given me direction on this issue. I enjoy all of your articles and have read many of them over and over trying to truly understand the relationships between all the variables in our home reefs.

 

[Griff]

I also know the fresh mix does not match the tank should I dose the freshly mixed salt water to match the tank?

 

[Randy Holmes-Farley]

Thanks. I've read that article many times. I think it's a bit over my head. Is it ok to just dose the Alk then, while keeping an eye on calc

Yes, that is fine.

 

[Randy Holmes-Farley]

I also know the fresh mix does not match the tank should I dose the freshly mixed salt water to match the tank?

Does it have less alk than the tank target? Many mixes have more than most folks maintain in their tank.

 

[arman]

I have read about Alkanity and other parameteres but i dont understand the difference between caco3 and bicarbonates and alkanity and relation to ca and mg.
Would you help me with a article.
I would be thankful.

 

[Griff]

Does it have less alk than the tank target? Many mixes have more than most folks maintain in their tank.

I am about to switch to redsea coral pro. I've been using redsea standard salt up to this point. Measured fresh batch and it comes out at 7.8 dkh. I'll test the first batch of the coral pro. According to the packaging it should be roughly 11dkh.