Need help, Randy are you out there

[mcfa2403]

I appreciate the response tmz and I will likely bring nitrates down again and see what happens. However, I want them to go down gradually so it might take a month or two.

 

[tmz]

I've though about adding a non-carbonate/borate base to raise pH- calcium or sodium hydroxide for example - but these are very strong bases with no real buffering ability which is making me a little cautious.

Those do add carbonate via the hydroxide joining CO2 to form CO3/HCO3; thus adding buffering capacity Borate is not a factor with those supplements. I've used calcium hydroxide(Ca(OH)2) as the primary/ almost always exclusive supplement for calcium and alkalinity in my system. When dosed slowly over the course of 24 hours it continuously uses CO2 in the water offsetting CO2 buildup from the surrounding air or otherwise. This article by Randy Farley has more:

http://reefkeeping.com/issues/2005-01/rhf/index.htm

The Ca provides the calcium ;these are the reactions noted for the OH - and CO2 .

"... OH^- + CO₂ à HCO₃^-
OH^- + HCO₃^- à CO₃^-- + H₂O ...."





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There is no plausible reason I can fathom to think fish deaths were caused by pH in the 7.7 to 7.9 range.There are a number of other potential causes: inlcuding ,disease.osmotic shock from a jump in salinity as examples.

 

[CHSUB]

The PO4 at around .3ppm seems high enough to alter the calcification process; ah ok reread ; 0.03 is certainly low enough( not sure a reading on the salifert test at that low a level is easily discerned though) .The NO3 also seems high; IME some sps fair poorly at those levels particualry seriatorpora.

However, the lower pH( higher CO2) might actually be helping overall given the higher NO3 as the study suggests . I don't know that since I don't run my aquariums that way but I suppose it's possible you might want even higher PO4 to enable the zoox to use the NO3.May be some iron too. This is an abstract from the study noted ion post #4


Zooxanthellate colonies of the scleractinian coral Astrangia poculata were grown under combinations of ambient and elevated nutrients (5 µM NO₃⁻, 0.3 µM PO₄^{− 3}, and 2 nM Fe^{+ 2}) and CO₂ (∼ 780 ppmv) treatments for a period of 6 months. Coral calcification rates, estimated from buoyant weights, were not significantly affected by moderately elevated nutrients at ambient CO₂ and were negatively affected by elevated CO₂ at ambient nutrient levels. However, calcification by corals reared under elevated nutrients combined with elevated CO₂ was not significantly different from that of corals reared under ambient conditions, suggesting that CO₂ enrichment can lead to nutrient limitation in zooxanthellate corals. A conceptual model is proposed to explain how nutrients and CO₂ interact to control zooxanthellate coral calcification. Nutrient limited corals are unable to utilize an increase in dissolved inorganic carbon (DIC) as nutrients are already limiting growth, thus the effect of elevated CO₂ on saturation state drives the calcification response. Under nutrient replete conditions, corals may have the ability to utilize more DIC, thus the calcification response to CO₂ becomes the product of a negative effect on saturation state and a positive effect on gross carbon fixation, depending upon which dominates, the calcification response can be either positive or negative. This may help explain how the range of coral responses found in different studies of ocean acidification can be obtained.

FWIW, I do not have the problems you noted with NO3 around 0.2ppm( per salifert) ,PO4 in the 0.02 to 0.04ppm range ( per hanah 713) and pH daily siwng 8.15 to 8.35( per pinpoint and milwaukee monitors with alk around 9dkh in a heavily fed system ;been solid for over 6 years this way .

excellent example of how problems are seldom just "X" and solutions are just "best guesses"? who would have thought that higher nutrients effects could be mitigated by lower pH!!! Gives more weight to the phrase, "every tank is different" and "there are things we don't know, we don't know" (D Rumsfeld). imo, follow how "mother nature" does it, she has been doing it long and better than any of us!!!

 

[GPHowell]

Those do add carbonate via the hydroxide joining CO2 to form CO3/HCO3; thus adding buffering capacity Borate is not a factor with those supplements. I've used calcium hydroxide(Ca(OH)2) as the primary/ almost always exclusive supplement for calcium and alkalinity in my system. When dosed slowly over the course of 24 hours it continuously uses CO2 in the water offsetting CO2 buildup from the surrounding air or otherwise. This article by Randy Farley has more:

http://reefkeeping.com/issues/2005-01/rhf/index.htm

The Ca provides the calcium ;these are the reactions noted for the OH - and CO2 .

"... OH^- + CO₂ à HCO₃^-
OH^- + HCO₃^- à CO₃^-- + H₂O ...."





​

There is no plausible reason I can fathom to think fish deaths were caused by pH in the 7.7 to 7.9 range.There are a number of other potential causes: inlcuding ,disease.osmotic shock from a jump in salinity as examples.

Ah, interesting, I hadn't thought about the hydroxide and carbonate equilibria interacting. Do you know what the equilibrium constants are for these two processes? They must be quite high, I guess, if kalkwasser is a common/safe additive.

I'm at a loss about the two fish deaths...

 

[blanden.adam]

Ah, interesting, I hadn't thought about the hydroxide and carbonate equilibria interacting. Do you know what the equilibrium constants are for these two processes? They must be quite high, I guess, if kalkwasser is a common/safe additive.

I'm at a loss about the two fish deaths...

There is no equilibrium constant for the CO2 hydroxide equilibrium as there isn't a direct reaction between them per-se. However, there is an equilibrium constant for the CO2 <--> H2CO3 = 1.2 x 10^-3 in seawater,

The rest of the equilibria are most easily described by their log affinity for protons (i.e. pKa) H2CO3 <---> H+ HCO3- (pKa1 = 3.6), HCO3- <--> H+ HCO3 2- (pKa2 = 10.3).

hydroxide has a pKa of 16 ish (so it binds protons 6 orders of magnitude tighter than bicarbonate, and 12 orders of magnitude tighter than carbonic acid), so it will take protons from all protic species in the equilibrium under all conditions you would encounter in a reef to make water (that's why your pH goes up). As a result, more CO2 dissolves to make up for the lost carbonic acid, and draws from the essentially infinite reservoir of CO2 from around the tank.

So, the net result is that hydroxide will more or less react to completion with CO2 (in the form of the carbonic acid-bicarbonate-carbonate equilibrium), and your CO2 supply is nearly unlimited.

 

[tmz]

Thanks Adam. Nice explanatrion.

I'd note, it's important to dose calcium hydroxide in small increments over time to allow time for CO2 to equilibriate from the air to the water and avoid pH spikes and precipitation.
Generally , a max of 1/4 tsp per 50 gallons of aquarium water volume per hour is safe.With typical top off needs that works out dosing fully saturated limewater ( 2tsps of calcium hydroxide per gallon of fresh water) at an amount approximately equal to daily top off in 5 or 6 increments at least an hour apart. Smaller increments over 24 hours are better . I dose it for top off in 150 increments about 9 minutes apart over 24 hours.