what, a low alk will allow orgaic acids to accumulate and that will cause a lower ph
That is not what I said, you are reading in to it.
I said
This can be done also from just the CO2 production from the organics with little /no effect on the Alk.
Meaning, organics can break down without producing acids and lower the pH from CO2 and if acids are involved it can be a double whammy. Meaning, one or the other or both. I added this to your correct comment
The normal effect usually for us is both CO2 and acid production form organics. However, there is no set rule that x or y organic during its break down can not just give off CO2 effecting pH and no acid or vise versa or do both. All organics don't give off acids, just like all organics don't give off CO2 and some yield both.
water with a very low alk will be more sensitive to CO2 and Pico
I'll say it again Alk has NO EFFECT on pCO2 changes. Show me a paper that says a lower Alk impacts a change in pCO2, its partial pressure for seawater or FW. However, if one wants to go off the Deep-6 end, then yes, as Alk is part of Salinity, as it is CO3--, HCO3-, Phosphates and Borates, which make up part of Salinity. Salinity effects the pCO2 as it causes a shift in the seawater pK1 and pK2, which are a function of Salinity and temp. In a reef tank there will be no such effect that can be measured. As I stated early, the only thing that may happen is the rate of pH drop, measured in time, from a Low Alk vs. High Alk, will be slower with higher Alk. This is not going to save your tank, unless maybe if we really stretch it, i.e., the Alk is about nil. And surely it is not going to happen with the comment by SeaLover "the alk is a little low" . His Alk is not 1 dkH.
what is your issue with this?
So, that is my issue
And to throw out this balance issue. Most reef tanks are out of balance, all one has to do is look at their water parameters. It is just the degree of balance. A Ca++ of 410 ppm and 2.45 meq / l is in Balance. And most run Alk higher than that like in the 3's, making them out of balance at that Ca++ level. What we ( you, me, Dave, others) call an imbalance is probably the same thing. You can't keep the Alk and or the Ca++ up. You try to fix it and it goes right back where it was. Do a water change and it goes away. This is usually from a low Mg++ or the continued addition of buffers at times where you are driving the tank chemistry to a new balance it wants based on solution kinetics from those additions. "Things" are leaving solution, which shifts the activity coefficients of all ions and the solution itself.
An ions wanting to be in solution or its wanting to leave solution is a function of their activity coefficients. This is why you can dissolve more Ca++ in seawater than FW or even table salt, NaCl. The increase in ions lowers the Ac, making it not to want to leave solution. If the ion concentration of the solution is less then the Ac goes up and things like to leave solution. Meaning, seawater has a very low Ac and FW has a very high Ac.
And just for the heck of it another balance issue. If you take well washed carbonate gravel and put it in a beaker of seawater, the pH, Alk and Ca++ will drop as the water and gravel are not in balance. If you now pull out that gravel and stick it under a microscope you will see Hi-Mg-Calcite growths on the gravel. This growth rate also depends on if it is Calcite, Aragonite or Dolomite gravel as the rates or growth are not the same. This usually stops in tanks as the gravel gets coated with organics.
We are lucky that our reef tanks do not precip Aragonite, for if they did we would have more issues. Aragonite does not care what the Mg++ level is . If the Mg++ drops low enough for Calcite it will continue to grow as a precip . Mg++ greatly slows the rate of growth for Calcite precip. However, if it was Aragonite growing it could care less what the Mg++ is and will continue to grow, as it is not effected by Mg++.
