What causes PH/Alk to drop?

koda_dad

Mr. Paranoid
Hi all,

I am a little confused... Hoping someone can shed some light on this topic for me. I apologize in advance if this doesn't make total sense :)

I know that PH changes throughout the day. But why does it fluctuate? What determine how much it will change? What determines the rate at which it changes?

Part 2.. Lets say over a week the Ph drops from say 8.4 - 7.8... so you add in a buffer to bring it back up... How long does this keep it at the new higher Ph? Is it the same as above that will then change the PH down again? The bottle of my buffer says apply daily.... just getting why.... What is the max ph change that is ok ad any one time?

As for Alk.... same kind of questions...if it is low and you do an additive to bring it up...I get you have to keep adding additives to keep it up.. but is that purely because of top ups? what other things bring it down?

Thanks
 
Funny how once you understand the chemistry and how everything works they all tie in together...

Quote from BL1's 2nd Article
There are two ways on maintaining pH level in its normal saltwater range.


First the saltwater itself has buffering capacity. It is the ability of a solution to resist changes in pH.
That "buffering capacity" is what is being measured when you test Alkalinity.

Keeping a good higher balance of Alkalinity/Calcium and your water will be more "resistant" to pH changes.

The test readings on your Alkalinity will fluctuate the most (according to the article I read) so you will have an easier time by keeping tabs on your Alkalinity; keep that in check and the others should be more manageable.

They suggest that Alkalinity should be the basis test for reefers (because it fluctuates the most) and intertwines together all; Alkalinity, Calcium, pH, Phosphate, and Magnesium.

They all work/connect together. If you can understand how those 5 work together and the nitration "cycle" (ammonia,nitrite,nitrate) then you understand Aquarium Chemistry :)

Check up my post I made the other day in this section about Alkalinity if you want to understand what I'm talking about.

Edit: P.S. They keep getting used up b/c organisms like your corals are using up those nutrients to grow. So you have to re supply your little Aquarium with whatever nutrients are getting depleted out of it. :)
 
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I know that PH changes throughout the day. But why does it fluctuate? What determine how much it will change? What determines the rate at which it changes?
The pH rises when the lights over your tank are on because photosynthesis is taking place and that process uses up the co2 in the water and causes the pH to rise. When the lights are off, no photosynthesis is taking place so co2 is building back up and pushing the pH back down. This is common and happens in everyone's system.
Lets say over a week the Ph drops from say 8.4 - 7.8... so you add in a buffer to bring it back up... How long does this keep it at the new higher Ph?
The pH will vary that much each day and is nothing to worry about. Buffers are a poor way to raise pH. They will have a longer lasting affect on pushing up your alkalinity (even to the point it's too high) than pushing up your pH. If your pH is either too high or too low, there are better ways to resolve that issue than using any type of buffer.
As for Alk.... same kind of questions...if it is low and you do an additive to bring it up...I get you have to keep adding additives to keep it up.. but is that purely because of top ups? what other things bring it down?
The best supplement to use to raise alk is Arm & Hammer baking soda. Alk gets used up, in a set ratio along with calcium and magnesium, in the calcification process. That process uses aprox 2.5 dKH alk for every 18 ppm calcium and 2 ppm magnesium. So if your system has the need for dosing alk, it also has the need for dosing calcium and magnesium. Alkalinity will only drop if it's being used up in the calcification process, if you water chemistry gets out of whack and you get a precipitation event in your system, or if you do water changes with a salt that has a lower alk level than your system.

This article should answer any other questions you may have.
A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH by Randy Holmes-Farley - Reefkeeping.com
 
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