Kalk dosing speed and pH impact

[ReefBeta]

Let's say I dose 200ml of kalk every 2 hours. First case dose 200ml kalk in 5 min, second case stretch out the dose to the whole 2 hours. Assuming a same starting pH, will the end pH in 2 hours be the same for both case?

 

[Garf]

Let's say I dose 200ml of kalk every 2 hours. First case dose 200ml kalk in 5 min, second case stretch out the dose to the whole 2 hours. Assuming a same starting pH, will the end pH in 2 hours be the same for both case?

Yeah, I think so because it will consuming the same amount of CO2. I like the slow as possible approach though.

 

[Lasse]

The first scenario will give you a high peak and slowly go down - the second scenario will give you a steady pH during the same time. IMO - use the second method.

Sincerely Lasse

 

[garbled]

You will remove the same quantity of CO2 in both scenarios, raising the pH by the same amount. Obviously in real life the numbers won't exactly line up, because unless your water is just a bucket, presumably your pH is rising and falling on it's own due to other tank things going on. The slower approach is better when possible, just because it keeps you from "shocking" the water in a way that the inhabitants might notice. This also depends alot on system size. In a 20 gal tank this is far more noticable than 1000g. My tank is big so I can get away with dumping in 250ml in a shot and not moving the pH much at all.

 

[litenyaup]

I dose right now 3500mls over 24 hr period in my 220. It does increase the ph only by .1-.15 as well as keep my alk stable. I’m getting close to my limit as I cannot exceed my top off water. I will soon start dosing aqua forest to keep parameters steady.

the kalk will increase ph but it takes a lot to make a huge difference. if u go too much your alk will supersede your consumption and sky rocket causing damage.

 

[Randy Holmes-Farley Verified Community Expert]

As folks have noted, adding hydroxide in any form (such as kalkwasser or my DIY two part ultra high pH recipe) consumes a fixed amount of CO2 per unit of alkalinity added, regardless of timing.

BUT, as soon as the tank is placed at a deficit of CO2 relative to the air, the tank begins to pull in CO2. If you dump a bunch of hydroxide, the pH jumps up and then falls back as the tank slowly pulls in more CO2. That might take hours, but not days.

IF you slowly spread out the same hydroxide addition, the jump is proportionally smaller each time, and the CO2 addition from the air is also spread out.

If you add it slowly enough (24/7 drip, for example), the tank will just average a slightly higher pH and you will not ever see a rise or fall back.

Which has the highest average pH over 24 h? I suspect it is the slow addition, but have not actually tried to measure it.

 

[ReefBeta]

As folks have noted, adding hydroxide in any form (such as kalkwasser or my DIY two part ultra high pH recipe) consumes a fixed amount of CO2 per unit of alkalinity added, regardless of timing.

BUT, as soon as the tank is placed at a deficit of CO2 relative to the air, the tank begins to pull in CO2. If you dump a bunch of hydroxide, the pH jumps up and then falls back as the tank slowly pulls in more CO2. That might take hours, but not days.

IF you slowly spread out the same hydroxide addition, the jump is proportionally smaller each time, and the CO2 addition from the air is also spread out.

If you add it slowly enough (24/7 drip, for example), the tank will just average a slightly higher pH and you will not ever see a rise or fall back.

Which has the highest average pH over 24 h? I suspect it is the slow addition, but have not actually tried to measure it.

So when dosing fast and have higher pH spike, the CO2 in the tank is lower than slow dosing. Tthe CO2 difference between the air is higher, thus the osmotic pressure higher, and lead to CO2 pulling back to the water faster? I most interested in how much the difference there would be.

For the reason of the question, I'm currently dosing kalk using the Kamoer X1 pump. It's set speed at 40ish ml/min. So I want to get an idea how much of an improvement it would be to smooth out the dose can bring, and if it justify the cost of it. The spike is about 0.03, so can I assume the improvement will be less than that? More like 0.01 improvement in average pH as an optimist guess?

 

[Randy Holmes-Farley Verified Community Expert]

So when dosing fast and have higher pH spike, the CO2 in the tank is lower than slow dosing. Tthe CO2 difference between the air is higher, thus the osmotic pressure higher, and lead to CO2 pulling back to the water faster? I most interested in how much the difference there would be.

For the reason of the question, I'm currently dosing kalk using the Kamoer X1 pump. It's set speed at 40ish ml/min. So I want to get an idea how much of an improvement it would be to smooth out the dose can bring, and if it justify the cost of it. The spike is about 0.03, so can I assume the improvement will be less than that? More like 0.01 improvement in average pH as an optimist guess?

Yes, although it is not "osmotic" pressure. It is concentration of CO2 in the water and the partial pressure of CO2 in the air.

The immediate pH spike is about 0.6-0.7 pH units for each 1.4 dKH added instantly to seawater. I'm not sure what you mean by the 0.03 pH units, unless that is from a very small addition.

 

[ReefBeta]

Yes, although it is not "osmotic" pressure. It is concentration of CO2 in the water and the partial pressure of CO2 in the air.

The immediate pH spike is about 0.6-0.7 pH units for each 1.4 dKH added instantly to seawater. I'm not sure what you mean by the 0.03 pH units, unless that is from a very small addition.

The 0.03 was the ph impact when adding 200ml kalk to a 180 gallon system. It drops back down after like 5 mins. Maybe it's local concentration though, since the pH probe is in the next chamber of where kalk went in.

I actual got to change up my kalk dosing. Now have a BRS doser continuously dosing, 1.1ml/m. Then adjusted the Kamoer X1 to dose 75ml instead of 200ml per two hours. It's basically the same among of Kalk every two hours. But the overall pH of the tank actually went up. The max pH up from 8.32 to 8.35. Had that same peak of 8.32 for at least last 4 days before the change.

The impact of slower dosing is more significant than I thought.