Got a Reef chemistry issue. Alk and Ca

[Capt_Cully]

Normally I'm not that excited about it, but as the tank is new, I've been testing every 1-3 days. I'm having an issue with the trend the tank is following.

My Alk is increasing regularly and my Ca is dwindling despite dosing 2-Part Recipie 1. I have them on dosers and have the Ca ahead of the Alk. At first it was slight, and now I'm running it even more out of balance. (yes I double checked to make sure I wasn't dosing the supplements in reverse)

My Ca had been hanging around 480 and Alk around 3.0. But in the last 3 weeks the alk has gone above 4 slowly and Ca has dwindled down to around 400-410.

If I'm dosing MORE Ca than Alk, what the heck is going on to achieve this trend????

Mg just now 1350
pH 8.10 and holding
Temp 78-79
Dosing 1.2 ml Vodka and 5.0ml Vinegar Daily
Weekly (without missing a week) Waterchanges with RC @ 1.025 SG


Normally I'm proud to handle these little conundrums, but this one has me scratching my head? What am I missing???? (just read through RHF's Ca/Alk article again, still nothing comes to mind)

 

[Conesus_Kid]

Hmmmm. How old are the test kits? Could you have mistakenly made the Ca portion too diluted? Just spitballing here...

 

[Capt_Cully]

kits are cross referenced with a new box. Same results.

Any way to test the Ca or alk components? I mixed per directions, but at least its a place to snoop around.

 

[pascal32]

Check how much the dosing pumps put out over 10 minutes and compare volumes. Also see if one the lines is "pulling back". I had a BRS pump that started doing this, so on frequent short doses hardly anything would come out because the line drained backwards each time.

From a chemistry perspective I'm not aware of what would cause that level of imbalance. Make sure both are mixed to the same recipe. Check your fresh salt mix.

 

[jeremyjoslin]

following along as the apprentice in Ca and Alk management....

From a chemistry perspective, is there another anion that could be consuming the Ca into a precipitate? Phos?

 

[Capt_Cully]

Pascal, I did that at set up. I also mark the jug every am to be sure that there are similar or expected volumes being dispensed.

Scratching my head on this one...

 

[pascal32]

Can you check your new salt to see if you got a batch with low CA? Also double. Heck the recipe #1 instructions for both to make sure you didn't pull in the recipe #2 instructions.

You using BRS chemicals?

I'll read up when I'm done assembling "engineered" bins for my daughters room to organize everything. I can't think of low CA off the top off my head, high there are reasons, but not what you are having.

 

[pascal32]

I poked around and am still miffed as to the root cause. Hopefully Tom can chime in and educate us!

Since your magnesium is good, for now I would slowly add CA and maintain the alkalinity supplement. as you move towards a balance the KH should lower. being that you are still "in the green" for CA I would use the reef calculator to add 25ppm per day of CA.

Note that this should lower your KH, as you reach a balance you might need to add equal parts to raise the overall values in the tank.

I'm still miffed as to how the CA can drop and KH go up when adding equal parts of two part while MG is good. Hoping Tom chimes in!

 

[tmz]

The salt Reef Crystals at 1.025 should mix to .96 of the values listed for 1.026. At 1.025 they should be: 470calcium, 12.5 /4.5meq/l alk, 1380 mag.. So depending on how big the water changes are the salt could play a significant role . The alk and mag in your tank look to be consistent with those levels,. The calcium is lower than expected. I'd check the salt mix newly mixed to see what the levels are. It's possible the salt in the buckett has los t homogeneity,i e, is unevenly mixed.

Other than the salt, something could be wrong with the dosing in terms of balance between alk and calcium or the testing .
Calcium will not deplete without alk depleting. It only takes 20ppm calcium to match 1 meq/l alk( ie, 2.8 dkh or 50ppm) in calcium carbonate precipitation. So alk goes down much faster than calcium unless the alk is being added in proportions greater than 50 ppm to 20ppm for calcium.
A drop of 70ppm calcium as noted would be accompanied by a drop of 175ppm carbonate which is 3.5meq l/ 9.8 dkh.
The magnesium will take the place of the calcium on some forming crystals and stop them from growing. This slows precipitation and conserves some calcium and allows you to keep more carbonate alkalinity and calcium in solution. But even without this reaction calcium is used at 20 ppm per 50ppm of carbonate alkalinity. It does not get used in any other way in a reeftank.

 

[tmz]

From a chemistry perspective, is there another anion that could be consuming the Ca into a precipitate? Phos

Phosphate is one of the elements that constitute alkalinity( a measure of the buffering capacity of the water, ie ability to neutralize acids) along with borate, carbonate ,bicarbonate and a few others.
96.5% of alkalinity in seawater is carbonate/ bicarbonte and there is no easy way to measure carbonate alkalinity separately so total alkalinity serves as a surrogate measure for it since we are primarily concerned about carbonate consumption by calcareous organisms. Some kits have a second step to help get a cleaner measure on carbonate alkalinity.
Even if PO4 were being used by calcium as a site it would still precipitate and not show up in the alk measure;ie total alkalinity would decrease whether calcium chose phosphate or carbonate to adsorb to.

 

[Capt_Cully]

I used to be a freak about testing new buckets of RCs after getting a bad batch that sent my tank for A loop. I also used to mix them upon opening by portioning them out into different buckets. Not a lot going in my tank now so I've been lax with these practices. I'll test some water I've got mixed for a water change today. I will review the mixing instructions, but, I JUST remixed my BRS jugs so the newly mixed stuff hasn't been around long enough to cause this separation in parameters. Furthermore, the old jugs were the same ones responsible for the stability before this abberant trend.

I have noted that my corral one growth has begun to take off which could account for some consumption but it SHOULD consume alk as well. I don't have a phosphate test kit, BUT , I'm headed to ABC today anyway, perhaps it's time.

FWIW nitrates are zero per Seachem test kit (new).

 

[Capt_Cully]

Appears another suspect batch of RC's is to blame.

Ca @ SG of 1.025 330! dKH was 10.0

I supplemented some Ca from BRS powder into the new batch of saltwater just before I did my weekly waterchange today to juice it up to about 480, which will be diluted by the other 85-90% of remaining water. Hopefully this will bring Ca up to 410 or so and my supplementation schedule will handle the rest. I may need to dose more of Ca and Alk all together, but at least I'm not wondering where the Ca was going all this time.

I'll continue testing and repost if it isn't the problem. But it is a reminder to check EVERY new bucket of RC's. This is twice for me. Don't want a third time. Also be sure to shake em up when you open them. I like to pour them into another empty bucket or two, then pour them simultaneously into the original bucket to remix it. Avoid additional problems.

 

[Gary Majchrzak]

Mark- it's time to switch from buckets of RC to boxes...

 

[Capt_Cully]

Not available locally. And @ $40 a bucket @ ABC Reefs......it's a price I can't refuse.

 

[pascal32]

Gary -

have you had better consistency with the boxes?

Cully -

glad you got it figured out!

 

[pascal32]

also if you haven't calibrated the refractometer against 35 ppt solution let me know, I have some.

 

[block head]

my issues are almost always linked to phosphate. once i get phos under control, everything else is relatively easy. i'd drop the 50 beans and buy a hanna. or at the very least, have tim test for you. ca,alk,mg numbers are fubared with high phosphate. controling phosphate forces you, to take care of rodi issues, rock/sand leaching, overfeeding, and overall water quality. IMO it's hard to screw up water chemistry when you take the steps to maintain low levels of phos.

 

[tmz]

For perspective,while I agree limiting inorganic phosphate is important for many reasons, it has little to do with alkalinity levels and calcium adsorbtion since even at "high" levels it is a relatively small portion( think .03ppm low level or a high levels of .5ppm vs 50ppm carbonate and 400ppm calcium for example) of the alkalinity .

Alkalinity is actually a measure of how much acid is needed to drop ph to 4.2. In seawater it is:96.5% carbonate/bicarbonate with borate, oxide, silicate, magnesium hydroxide and orthophosphate making up the remaining 3.5% with phosphae teh least of these by a lot.

Phosphate is only .1% fo total alk in seawater.

This table from Randy Farely's article entitled "What is alkalinity" may be of interest:

<table id="table1" class="listing nosort"><thead><tr><th>Chemical Species</th> <th>Relative Contribution To Alkalinity</th> </tr> </thead> <tbody> <tr> <td>HCO₃^- (bicarbonate)</td> <td>89.8</td> </tr> <tr> <td>CO₃^-- (carbonate)</td> <td>6.7</td> </tr> <tr> <td>B(OH)₄^- (borate)</td> <td>2.9</td> </tr> <tr> <td>SiO(OH)₃^- (silicate)</td> <td>0.2</td> </tr> <tr> <td>MgOH⁺ (magnesium monohydroxylate)</td> <td>0.1</td> </tr> <tr> <td>OH^- (hydroxide)</td> <td>0.1</td> </tr> <tr> <td>HPO₄^-- and PO₄^--- (phosphate)</td> <td>0.1</td></tr></tbody></table>

 

[Capt_Cully]

By what means do you measure phosphates Tom? Hanna? If so, does it require frequent calibration? Or do you use test kits? Thanks?

 

[pascal32]

None of the phosphate measuring tools which we can afford are super accurate. IMO the best that is out there is the hanna phosphorous (ULR) - this is NOT the same as teh phosphate unit that BRS sells (same color, but not the same). They calibrate themselves, so no calibration is needed.

here is a thread on the two:

http://reefcentral.com/forums/showthread.php?t=2066574&highlight=hanna