Alkalinity stability? pH stability? Are they even different?

drawman · Apr 22, 2020

Nhjmc said:
I am new to hobby. Struggling to understand and get correct. So frustrating. In the last six months I’ve read probably 500 articles/posts/blogs joined several groups on Facebook and watched hundreds of youtube videos on reefkeeping. Probably gonna sound really dumb to most people that are advanced in this hobby but I’m struggling. Idk what I’m doing wrong. My alk tested 12-12.5 I tested twice with brand new salifert kit good till 2024 (Hanna alk check on order thank god) ca 550 mg 1290 but can’t get my ph over 8.0. I did a 5 gal water change hoping that helps. I have a RSM 130d.

Depending on what you're trying to keep your Calcium and Alkalinity are quite elevated. I would get your calcium closer to 420-450 and some coral (ie sps) tend to be easier to keep around 7-9dKh. In your scenario pH would not be the first thing I would be looking at. What salt are you using and what are you trying to keep?

dustinc · Apr 22, 2020

I'm really working to try and keep my pH stable in my tank. I'm to the point that with a CO2 scrubber hooked to my skimmer, I can have it range between 7.85-7.9 total (media lasts about 1 week). I really struggle to get it any higher. I have my parameters stable at 8.6 dkH, 480 calcium, and 1440 mag and the tank is currently rock and fish only, soon to start adding corals. I have a lot of surface agitation as well in the setup with (4) MP40s going as it will be an Acro dominant setup (bare-bottom). Any other suggestions to get the pH a bit higher and maintain that? It's a 2019 built home with foam insulation and have no way to effectively get outside air to the tank, although that makes a small difference, not a major one.

I'm also planning to dose the DIY Tropic Marin All for Reef once I start needing a consistent dosing schedule after adding corals. Will this have any affect on pH, positive or negative? I'm open to any and all suggestions.

Thank you.

P.S. I've read your linked articles about pH as well.

Brendank · Apr 22, 2020

Nhjmc said:
I am new to hobby. Struggling to understand and get correct. So frustrating. In the last six months I’ve read probably 500 articles/posts/blogs joined several groups on Facebook and watched hundreds of youtube videos on reefkeeping. Probably gonna sound really dumb to most people that are advanced in this hobby but I’m struggling. Idk what I’m doing wrong. My alk tested 12-12.5 I tested twice with brand new salifert kit good till 2024 (Hanna alk check on order thank god) ca 550 mg 1290 but can’t get my ph over 8.0. I did a 5 gal water change hoping that helps. I have a RSM 130d.

Randy, correct if I’m mistaken but this sounds like a symptom of high ambient CO2. Try keeping the windows open in your home for a day and see if the pH goes up at all.

Randy Holmes-Farley · Apr 22, 2020

Brendank said:
Randy, correct if I’m mistaken but this sounds like a symptom of high ambient CO2. Try keeping the windows open in your home for a day and see if the pH goes up at all.

Exactly. It is perfectly normal for an aquarium that is in a high CO2 environment.

Randy Holmes-Farley · Apr 22, 2020

Nhjmc said:
I am new to hobby. Struggling to understand and get correct. So frustrating. In the last six months I’ve read probably 500 articles/posts/blogs joined several groups on Facebook and watched hundreds of youtube videos on reefkeeping. Probably gonna sound really dumb to most people that are advanced in this hobby but I’m struggling. Idk what I’m doing wrong. My alk tested 12-12.5 I tested twice with brand new salifert kit good till 2024 (Hanna alk check on order thank god) ca 550 mg 1290 but can’t get my ph over 8.0. I did a 5 gal water change hoping that helps. I have a RSM 130d.

My suggestion is to start a new thread in this forum on pH issues, rather than mix it in with this discussion. There are lots of ways to raise pH, and it may not change anything in your tank if you do so. Water changes aren't useful for pH control.

bubbaque · Apr 22, 2020

Randy on your chart it shows the higher the ph the lower the bicarbonate dkh.

If corals use bicarbonate why would anyone want higher ph if it lowers their bicarbonate level?

Randy Holmes-Farley · Apr 22, 2020

bubbaque said:
Randy on your chart it shows the higher the ph the lower the bicarbonate dkh.

If corals use bicarbonate why would anyone want higher ph if it lowers their bicarbonate level?

Experimentally, higher pH appears to accelerate calcification for some corals. The question is why.

It might be because it is much easier to pump out the H+ needed for calcification (for two reasons, to convert bicarbonate into carbonate, and to otherwise raise the pH in the region of the coral where calcium carbonate deposition is actually taking place).

It might also be, as mentioned above, that corals might actually take up carbonate, despite the evidence suggesting it is bicarbonate.

Brendank · Apr 22, 2020

I think it’s pretty well accepted in the academic literature that most calcifying coral species probably accelerate growth under elevated pH. However like I mentioned before, studies that show otherwise generally aren’t published as often or are harder to find due to publication bias. There are a few species that essentially without question are immune to mild acidification.

Shawn_epicurious · Apr 22, 2020

I just realized the depth of what I don’t know... wow.

Lasse · Apr 23, 2020

When we are talking about pH we are normal not aware that the pH scale is logarithmic. It means that the hydrogen concentration (H+) (actually the hydronium concentration (H3O+) ) at pH 7 have 10 times more H ions (H3O ions) compared with pH 8. If we compare pH 8.3 and pH 8.0 - PH 8 have nearly 2 times more hydrogen ions (hydronium ions) compared with pH 8.3.

@Randy Holmes-Farley statement below maybe not - in the first thoughts - mean so much if the pH increase "only" goes from 8 to 8.3

Randy Holmes-Farley said:
It might be because it is much easier to pump out the H+ needed for calcification (for two reasons, to convert bicarbonate into carbonate, and to otherwise raise the pH in the region of the coral where calcium carbonate deposition is actually taking place).

But - at the second thought - it cost energy if you have to pump against a gradient - energy that can be used for other purposes. The "contra pressure" will nearly double if you go from 8.3 to 8.0. Compare with the energy input you have to do if you lift 20 kg stone compared with one at 10 kg.

Next step - in this model HCO3 is used as an inorganic carbons source for both photosynthesis and calcifiering. It cost energy (to convert HCO3 to CO2 (photosynthesis) and to convert HCO3 to CO3 (calcification)) - Further on - the process will work into an acidification of the tank water but will be contradicted (total or partly) of a tendency for CO3 to be converted to HCO3 if the pH go down - buffering capacity)

When I read @Randy Holmes-Farley ´s statement and the article I linked to in post #36 I feel rather sure of what process is the major pathway for at least the calcification process. But - and a large but - there is on very obvious fact that every reefer know that bother me.

Why do we see a pH rise when the photosynthesis work fully out if HCO3 is the major pathway for both processes?

If the calcification process use CO3 we would have a tendency of pH decrease. The consumption of pure CO3 will force the buffer system to convert HCO3 into CO3 - liberating one hydrogen (hydronium) ion into the water. This is not my problem

As I see it - if our organisms major pathway is to use HCO3 as inorganic C source both for photosynthesis and calcification - this process is at least pH neutral - this is my real problem - because in an experimental way - the photosynthesis process drive up the pH rather much.

Lets go back to the photosynthesis - this process (on molecular level) need CO2 as inorganic carbon source. CO2 is a gas and gases can diffuse in or out of many cells and tissues. It a passive transport driven by gradients - not any energy costly process against gradients.

In my world - if CO2 is present - the most cost effective process for the whole process of photosynthesis would be to use available CO2 in first hand and transfer to a more energy costly process when the CO2 get sparse. If the organism use CO2 already present in the water - the pH will rise in a closed system. My explanation to all this is that the photosynthesis of the corals use of CO2 as first choice is in line with the natural princip of always use the most cost effective method of energy use. When CO2 decrease in our aquarium the natural equilibrium point of CO2 between the air and water tend to give an injection of CO2 into the water but this is normally a rather slow process compared with the photosynthetic process consumption of CO2 in a closed system.

This means that the fast rise in pH during photosynthesis can be caused of CO2 uptake into the photosynthesis process and everything we see experimental make sense. If there is no CO2 uptake - I can't explain the pH rise. I have also noted that there seem to be a maximal pH during day - and many times the same in spite of the night pH.

Where do I stand now? From what i know now - I lean to believe that there is a "sweet point” there the energy demand for using HCO3 in calcification even out with the energy gain into using CO2 (instead of using HCO3) for photosynthesis. This “sweet point” will be expressed as a certain pH. Exactly which – no idea but I have a feeling that it could be somewhere around 8.15. This means that – in this imagined point – the energy balance is optimal. It does not mean that it is optimal for the organism itself – but for the energy balance in order to maximize input relative to output. It gets maximal energy for other tasks. Growth of soft tissue as an example. Another way to maximize the metabolism of the animal is to rise the temperature. In the last few years there have been many experiments both in vivo and vitro looking at the relationship between rising temperatures and declining pH for corals health. All studies I have seen indicate such a relationship and that 1 + 1 will be higher than 2 in such cases. That this probably is not true for 100 % of corals species (or individual clones) and it is another case and have nothing with the big picture to do. As a friend use to say when some not expected and odd things happen in biological systems – there is idiots everywhere.

However – for many years I have been thinking of to do a system where pH should be fixed at (as an example) 8.15 and see if I could get an optimal growth of my corals. A little bit in line with the first post in this thread – what´s happen if we try to have the pH stabile instead of KH. During photosynthesis I need to add CO2 and during dark respiration – I need to take out CO2.

@Randy Holmes-Farley - My question is if you can supplement your excellent table with the amount of CO2 in the different pH and 8 dKH in alkalinity.

I have no idea if my thoughts are crazy or not but look forward to if others can confirm or reject the ideas. As I mentioned before – we get some unexpected results with S.hystrix grown in different pH. We did construct that system in a way there the pH was constant and not jump up and down along a hysteresis curve. The pH variation was in the plus – minus 0.01 variation. During photosynthesis - it was lowered with CO2. During dark metabolism - it was raised with help of aeration and CO2 free air

Sorry for long post but this is probably not main street thoughts - I need to explain my self

Sincerely Lasse

Randy Holmes-Farley · Apr 23, 2020

Lasse said:
@Randy Holmes-Farley - My question is if you can supplement your excellent table with the amount of CO2 in the different pH and 8 dKH in alkalinity.

Sure. I jus thave to add some columns to my excel spreadsheet. Wikipedia shows the equations I'll use under "Bjerrum Plot"

Randy Holmes-Farley · Apr 23, 2020

As expected, a drop of 0.3 pH units is about a doubling of CO2.

pH	HCO3- (dKH)	CO3— (dKH)	CO2 (in “dKH”)
7.60	7.54	0.28	0.1324
7.65	7.52	0.31	0.1170
7.70	7.49	0.35	0.1033
7.75	7.46	0.39	0.0911
7.80	7.42	0.44	0.0803
7.85	7.37	0.49	0.0706
7.90	7.31	0.54	0.0621
7.95	7.25	0.61	0.0544
8.00	7.18	0.67	0.0477
8.05	7.10	0.75	0.0417
8.10	7.01	0.83	0.0364
8.15	6.92	0.92	0.0317
8.20	6.81	1.01	0.0275
8.25	6.70	1.12	0.0239
8.30	6.57	1.23	0.0207
8.35	6.44	1.35	0.0178
8.40	6.29	1.48	0.0153
8.45	6.13	1.62	0.0131
8.50	5.97	1.77	0.0112
8.55	5.79	1.93	0.0096
8.60	5.60	2.09	0.0081

Wtyson254 · Apr 23, 2020

Randy Holmes-Farley said:
As expected, a drop of 0.3 pH units is about a doubling of CO2.

pH HCO3- (dKH) CO3— (dKH) CO2 (in “dKH”)
7.60
7.54
0.28
0.1324
7.65
7.52
0.31
0.1170
7.70
7.49
0.35
0.1033
7.75
7.46
0.39
0.0911
7.80
7.42
0.44
0.0803
7.85
7.37
0.49
0.0706
7.90
7.31
0.54
0.0621
7.95
7.25
0.61
0.0544
8.00
7.18
0.67
0.0477
8.05
7.10
0.75
0.0417
8.10
7.01
0.83
0.0364
8.15
6.92
0.92
0.0317
8.20
6.81
1.01
0.0275
8.25
6.70
1.12
0.0239
8.30
6.57
1.23
0.0207
8.35
6.44
1.35
0.0178
8.40
6.29
1.48
0.0153
8.45
6.13
1.62
0.0131
8.50
5.97
1.77
0.0112
8.55
5.79
1.93
0.0096
8.60
5.60
2.09
0.0081

What is the conversion for CO2 dKH to PPM?

Randy Holmes-Farley · Apr 23, 2020

Wtyson254 said:
What is the conversion for CO2 dKH to PPM?

1 dKH = 0.17832 mmole per litre

when referring to CO2, 1 mmole = 44 mg

so 1 dKH = 7.8 mg/l

Brendank · Apr 23, 2020

The coral itself may also be supplying CO2 for photosynthesis from its metabolic processes.

Brendank · Apr 23, 2020

Lasse, when combined effects, most especially water temperature gets into the discussion we must be EXTRA careful about information sources. There is A LOT of propaganda even amongst peer-reviewed academic publications on the effect of water temperatures on coral health.

Lasse · Apr 23, 2020

Brendank said:
The coral itself may also be supplying CO2 for photosynthesis from its metabolic processes.

Sure - but will not give a rise of pH in the water column - IMO - and therefore of no interest in my thought in above post.

And by the way - stop fishing - I will not take the bait in this thread

Sincerely Lasse

Lasse · Apr 23, 2020

Randy Holmes-Farley said:
Sure. I jus thave to add some columns to my excel spreadsheet. Wikipedia shows the equations I'll use under "Bjerrum Plot"

Randy Holmes-Farley said:
As expected, a drop of 0.3 pH units is about a doubling of CO2.

pH HCO3- (dKH) CO3— (dKH) CO2 (in “dKH”)
7.60
7.54
0.28
0.1324
7.65
7.52
0.31
0.1170
7.70
7.49
0.35
0.1033
7.75
7.46
0.39
0.0911
7.80
7.42
0.44
0.0803
7.85
7.37
0.49
0.0706
7.90
7.31
0.54
0.0621
7.95
7.25
0.61
0.0544
8.00
7.18
0.67
0.0477
8.05
7.10
0.75
0.0417
8.10
7.01
0.83
0.0364
8.15
6.92
0.92
0.0317
8.20
6.81
1.01
0.0275
8.25
6.70
1.12
0.0239
8.30
6.57
1.23
0.0207
8.35
6.44
1.35
0.0178
8.40
6.29
1.48
0.0153
8.45
6.13
1.62
0.0131
8.50
5.97
1.77
0.0112
8.55
5.79
1.93
0.0096
8.60
5.60
2.09
0.0081

Randy Holmes-Farley said:
1 dKH = 0.17832 mmole per litre

when referring to CO2, 1 mmole = 44 mg

so 1 dKH = 7.8 mg/l

Thank you very much

Sincerely Lasse

Wtyson254 · Apr 23, 2020

Lasse said:
Sure - but will not give a rise of pH in the water column - IMO - and therefore of no interest in my thought in above post.

And by the way - stop fishing - I will not take the bait in this thread

Sincerely Lasse

In some way corals/photosynthesis is taking up H+ during the day....