dKH without pH

[huey_gnr]

I have read a wide variety of articles and differing opinions on this one, but I am going to post this to see if perhaps someone has something that makes more sense to me than what I am seeing.

Bottom Line: My dKH progressively drops throughout the week if I do not dose. ~ loss of .2 dKH per 24 hours However, the corresponding pH change does not drop at a rate that would allow me to dose and keep things level without skyrocketing the pH levels.

For example, please see the below measurements.

Wed dKH - 8.0 pH - 8.3
Tue dKH - 7.8 pH 8.2
Thur dKH - 7.7 pH 8.0
Dose 1 fl oz soda ash solution
Fri dKH - 8.0 pH 8.4

And so it goes... I want to maintain my dKH at 8.0 and my pH around 8.3 +/- .1. But if I made small daily additions of soda ash, my pH would climb higher than I would like.

Is there a way to maintain the dKH where I want without the corresponding increase in pH?

Other levels that I maintain consistently are:

Salinity 1.024 / Temp 79 / PO4 0 - 0.1 / NO2 0 / NO3 0 - 0.1 / Ca 430 / Mg 1300 / Ammonia as close to 0 as I can maintain

It is a 75 gallon mixed tank. Running Bubble Magus Curve 5 Skimmer w/ CO2 scrubber, 200 micron filter sock, standard black filter, 2 chemi pure elite bags rated for 50 gal per and a few brightwell bio blocks. Tank has been set up for ~ 6 months 'ish.

Thanks in advance.

 

[kharmaguru]

PH is predominantly effected by CO2 as you've obviously realised by including the scrubber. PH should be fine up to 8.6.

Switch from Soda ash to sodium bicarbonate (baking soda) will maintain your DKH without a PH boost. In fact there will be temperary PH drop.

Here's a calculator:

Reef Chemistry Calculator

 

[mtnbike101]

You have an issue most of us desire! A pH of 8.4 is fine; you will get faster coral growth.

Have you tried dosing lesser amounts of soda ash daily? How high does pH climb?

If you really want to cap pH, dose sodium bicarbonate instead of soda ash. It does not have quite the impact on pH.

 

[huey_gnr]

PH is predominantly effected by CO2 as you've obviously realised by including the scrubber. PH should be fine up to 8.6.

Switch from Soda ash to sodium bicarbonate (baking soda) will maintain your DKH without a PH boost. In fact there will be temperary PH drop.

Here's a calculator:

Reef Chemistry Calculator

Thanks. For some reason I had it in my head backwards that bicarbonate impacted pH and ash did not. I will give it a go. Thanks.

 

[huey_gnr]

You have an issue most of us desire! A pH of 8.4 is fine; you will get faster coral growth.

Have you tried dosing lesser amounts of soda ash daily? How high does pH climb?

If you really want to cap pH, dose sodium bicarbonate instead of soda ash. It does not have quite the impact on pH.

Once the pH starting getting close to 8.6 I stopped the daily dosing and went with what I posted above of a 3 day correction. But, I will give the bicarbonate a go. Thanks!

 

[wq-viz]

Switch from Soda ash to sodium bicarbonate (baking soda) will maintain your DKH without a PH boost. In fact there will be temperary PH drop.

I've got a blog post on the effect of bicarb on pH and [Alk] in recirc aquaculture (RAS). (I'm prepping one on sodium carbonate.)

FYI, depending on the species/system, adding bicarb either raises, lowers, or -- as in the case you addressed -- hardly increases pH at all.

That last case has confused more than a few RAS aquaculturists who think that bicarb always raises pH. Unchecked, a few have inadvertently increased [Alk] to more than six times the standard seawater level.

 

[cal_stir]

You could dose at night when ph is lower