Aquarium pH Distilled

[arking_mark]

I just wanted to share my understanding of reef pH which is mostly based on:

Low pH: Causes and Cures by Randy Holmes-Farley - Reefkeeping.com

Many would agree that reef tanks can be successful with pH between 7.8 – 8.5 NBS and daily swings as great as 0.5 NBS.

Natural pH levels in our ocean reefs are typically 8.1-8.2 NBS

pH/Alk/CO2 have a defined relationship. So given any two of these parameters, you can calculate the third. This also means that your pH is determined by your tank's CO2 and Alk levels. It should be noted that the addition or subtraction of CO2 does not impact Alk levels. So essentially, in our Alk stabilized systems effective CO2 determines pH.

A tank’s effective CO2 level is determined by CO2 sources (inputs) and sinks (outputs).

The main sources of CO2 are indoor CO2 levels and livestock. The main sinks of CO2 are photosynthetic organisms such as algae.

Indoor CO2 levels around a tank are typically between 600 – 1200 matm and can vary greatly throughout the day depending on # of people in the room/house airflow and the amount of outdoor air exchange. Outdoor CO2 levels are typically around 400 matm.

As an example, let’s say your effective CO2 level swings from 1200-600 matm and you keep your Alk stable at 8dKH. Your pH will swing from 7.85 to 8.12. If instead, you keep your Alk at 11 dKH then you’ll see your pH swing from 7.98 to 8.23.

In our small closed system tanks, it’s certainly possible to have much lower effective CO2 levels with poor circulation and/or heavy livestock stocking. Similarly, with heavy photosynthetic organisms, you can see much higher pH levels during the light cycle.

CO2 Scrubbers and high-pH additives (usually hydroxides such as Kalkwasser) can be CO2 sinks. It’s important to note that high-pH dosing effects are temporary as it results in removing a specific amount of Hydrogen whereas the CO2 sources (that increase H) such as your indoor CO2 levels will continually work to achieve equilibrium. Basically, pH buffers are very temporary (hrs) and add stuff that will eventually unbalance your tank. These are not good solutions for maintaining pH.

Calcium Carbonate reactors and low-pH additives can be CO2 sources.

Insufficient tank aeration will also result in CO2 accumulation in the tank.

A simple cup aeration test can help determine why you have low pH in your tank.

Methods that raise pH:

• Keeping air around your tank/skimmer moving and well exchanged with appropriate CO2 level air (open windows, air exchange systems, outdoor air connected skimmers, CO2 Scrubber connected skimmers, etc…)
• Increase photosynthetic organisms in the tank such as macroalgae (Refugium with macroalgae running on a reverse lighting schedule will provide a boost at night to reduce common day/night swings)
• High-pH dosing such as Kalkwasser drip

pH can be controlled with a pH monitor and controlled CO2 scrubber and/or controlled high-pH additive dosing (this is more complex as you have to account for what else is being dosed such as Ca/Alk if you are using Kalkwasser).

I hope this helps others. Please feel free to let me know if I missed anything.

 

[lapin]

nice write up

 

[arking_mark]

I wanted to add a little information on realistic pH measurements and what to believe.

Assuming good tank aeration with no other contributors to tank CO2, meaning your tank is in simple equilibrium with your home CO2 levels. We can look at typical CO2 air quality and see reasonably expected pH values.

So let's go with low Alk for worst-case scenarios...6 Alk
400 --> 8.15 NBS
800 --> 7.9 NBS
1000 --> 7.8 NBS
1500 --> 7.67 NBS
2000 --> 7.55 NBS

So with Alk at 7 we get:
400 --> 8.2 NBS
800 --> 8.0 NBS
1000 --> 7.9 NBS
1500 --> 7.7 NBS
2000 --> 7.6 NBS

So if you are getting readings 7.7 and below, really consider 2 things. Either your test kit is off or your indoor air quality is really bad. Most of the time, indoor air quality is between 600-1200...so it's usually your test kit. Don't believe your measurements if they don't fall within the realm of reason

 

[Kayanarka]

I wanted to add a little information on realistic pH measurements and what to believe.

Assuming good tank aeration with no other contributors to tank CO2, meaning your tank is in simple equilibrium with your home CO2 levels. We can look at typical CO2 air quality and see reasonably expected pH values.

So let's go with low Alk for worst-case scenarios...6 Alk
400 --> 8.15 NBS
800 --> 7.9 NBS
1000 --> 7.8 NBS
1500 --> 7.67 NBS
2000 --> 7.55 NBS

So with Alk at 7 we get:
400 --> 8.2 NBS
800 --> 8.0 NBS
1000 --> 7.9 NBS
1500 --> 7.7 NBS
2000 --> 7.6 NBS

So if you are getting readings 7.7 and below, really consider 2 things. Either your test kit is off or your indoor air quality is really bad. Most of the time, indoor air quality is between 600-1200...so it's usually your test kit. Don't believe your measurements if they don't fall within the realm of reason

What if your worried a jealous spouse might drop muriatic acid tablets in the tank while your at work, so your testing ph nightly, that would explain a high reading with normal room co2 levels.

 

[arking_mark]

What if your worried a jealous spouse might drop muriatic acid tablets in the tank while your at work, so your testing ph nightly, that would explain a high reading with normal room co2 levels.

Lol. I heard a story that a Reefer was able to catch a cheating spouse by monitoring pH and figuring out why his pH kept dipping while he was at work.

 

[lagnew904]

Three days into cycle. Red sea is reading 7.6 pH and hanna is reading 7.3 DKH.

Testing control batch of salt water red sea is 8.0 pH and hanna is 7.3 DKH.

Tropic marin pro reef salt and good water surface agitation. Will open windows and check Co2 when meter gets in from amazon.

 

[MnFish1]

If you calibrate you pH meter to 4, 7, and 10. And it reads 7.6 (with windows open and alkalinity of 8 - how would you explain that?

 

[Randy Holmes-Farley]

If you calibrate you pH meter to 4, 7, and 10. And it reads 7.6 (with windows open and alkalinity of 8 - how would you explain that?

Inadequate aeration of the aquarium water, with accumulated CO2 in the water, can explain that. That's why my aeration test includes both inside and outside air:

The Aeration Test

Some of the possible causes of low pH listed above require an effort to diagnose. Problems 3 and 4 are quite common, and here is a way to distinguish them. Remove a cup of tank water and measure its pH. Then aerate it for an hour with an airstone using outside air. Its pH should rise if it is unusually low for the measured alkalinity (Figure 2). Then repeat the same experiment on a new cup of water using inside air. If its pH also rises, then the aquarium’s pH will rise simply with more aeration because it is only the aquarium that contains excess carbon dioxide. If the pH does not rise in the cup (or rises very little) when aerating with indoor air, then that air likely contains excess CO2, and more aeration with that same air will not solve the low pH problem (although aeration with fresher air should). Be careful implementing this test if the outside aeration test results in a large temperature change (more than 5°C or 10°F), because such changes alone impact pH measurements.

 

[arking_mark]

If you calibrate you pH meter to 4, 7, and 10. And it reads 7.6 (with windows open and alkalinity of 8 - how would you explain that?

If your pH is less than 7.8, it can be from the following causes:

1. Inadequate tank aeration that leads to the accumulation of CO2
2. pH-lowering dosing such as a calcium carbonate reactor
3. Super-high stocking levels that would cause in-tank issues
4. Unhealthy levels of CO2 in your tank location or house that would cause you noticeable health issues

#3 & #4 are super unlikely as you would notice these issues. #4 would cause you health issues such as headaches, lethargy, etc... These are super easy to rule out and super uncommon.

So if your tank has good aeration, your house or tank area has normal indoor levels of CO2, your tank is not super overstocked, and you are not dosing anything that lowers pH, any reading below 7.8 is not accurate. Your meter is not giving a realistic number.

 

[MnFish1]

Inadequate aeration of the aquarium water, with accumulated CO2 in the water, can explain that. That's why my aeration test includes both inside and outside air:

The Aeration Test

Some of the possible causes of low pH listed above require an effort to diagnose. Problems 3 and 4 are quite common, and here is a way to distinguish them. Remove a cup of tank water and measure its pH. Then aerate it for an hour with an airstone using outside air. Its pH should rise if it is unusually low for the measured alkalinity (Figure 2). Then repeat the same experiment on a new cup of water using inside air. If its pH also rises, then the aquarium’s pH will rise simply with more aeration because it is only the aquarium that contains excess carbon dioxide. If the pH does not rise in the cup (or rises very little) when aerating with indoor air, then that air likely contains excess CO2, and more aeration with that same air will not solve the low pH problem (although aeration with fresher air should). Be careful implementing this test if the outside aeration test results in a large temperature change (more than 5°C or 10°F), because such changes alone impact pH measurements.

Hi - thanks - I didnt make my question clear. I am aware that aeration (i.e. dissolved CO2) in the water will affect the pH. The question related more to 'is there any time where the Alkalinity, pH and CO2 relationship can be askew. So - lets I'll use different numbers than in my original question lets say the alkalinity is 10, the CO2 levels are low (i.e. maximally aerated), would there be any possibility for the pH to be lets say 7.5. Or by definition would it have to be higher. (My strong assumption is the pH would have to be higher). I was just curious

 

[MnFish1]

If your pH is less than 7.8, it can be from the following causes:

1. Inadequate tank aeration that leads to the accumulation of CO2
2. pH-lowering dosing such as a calcium carbonate reactor
3. Super-high stocking levels that would cause in-tank issues
4. Unhealthy levels of CO2 in your tank location or house that would cause you noticeable health issues

#3 & #4 are super unlikely as you would notice these issues. #4 would cause you health issues such as headaches, lethargy, etc... These are super easy to rule out and super uncommon.

So if your tank has good aeration, your house or tank area has normal indoor levels of CO2, your tank is not super overstocked, and you are not dosing anything that lowers pH, any reading below 7.8 is not accurate. Your meter is not giving a realistic number.

I just responded to Randy - I get all of that. that wasn't the question. I was asking is there anything else possible (besides CO2 and alkalinity, that can shift the pH relationship between the 2 items). My guess is there is not, that the relationship is fixed (i.e. if CO2 goes up, pH will go down - at a given alkalinity level.

 

[Randy Holmes-Farley]

Hi - thanks - I didnt make my question clear. I am aware that aeration (i.e. dissolved CO2) in the water will affect the pH. The question related more to 'is there any time where the Alkalinity, pH and CO2 relationship can be askew. So - lets I'll use different numbers than in my original question lets say the alkalinity is 10, the CO2 levels are low (i.e. maximally aerated), would there be any possibility for the pH to be lets say 7.5. Or by definition would it have to be higher. (My strong assumption is the pH would have to be higher). I was just curious

Certainly. There are folks with incomplete tank aeration so the tank water is not in equilibrium with the air. The tank can have excess CO2 or a deficiency in CO2. In fact, most tanks do, or else the pH would not change day to night, but only when the room CO2 changed.

It was true in my tank with elevated pH from using limewater (kalkwasser).

 

[Randy Holmes-Farley]

I just responded to Randy - I get all of that. that wasn't the question. I was asking is there anything else possible (besides CO2 and alkalinity, that can shift the pH relationship between the 2 items). My guess is there is not, that the relationship is fixed (i.e. if CO2 goes up, pH will go down - at a given alkalinity level.

There is nothing else besides CO2 (in the water, not the air) and carbonate alkalinity that determine pH (well, minor effects from temp and salinity). pH, alk, and CO2 in the water are related mathematically.

 

[Reef.]

I wanted to add a little information on realistic pH measurements and what to believe.

Assuming good tank aeration with no other contributors to tank CO2, meaning your tank is in simple equilibrium with your home CO2 levels. We can look at typical CO2 air quality and see reasonably expected pH values.

So let's go with low Alk for worst-case scenarios...6 Alk
400 --> 8.15 NBS
800 --> 7.9 NBS
1000 --> 7.8 NBS
1500 --> 7.67 NBS
2000 --> 7.55 NBS

So with Alk at 7 we get:
400 --> 8.2 NBS
800 --> 8.0 NBS
1000 --> 7.9 NBS
1500 --> 7.7 NBS
2000 --> 7.6 NBS

So if you are getting readings 7.7 and below, really consider 2 things. Either your test kit is off or your indoor air quality is really bad. Most of the time, indoor air quality is between 600-1200...so it's usually your test kit. Don't believe your measurements if they don't fall within the realm of reason

How do you define “good tank aeration”?

good post!

 

[arking_mark]

How do you define “good tank aeration”?

good post!

Using @Randy Holmes-Farley cup aeration test will yell you if your tank has enough aeration.

 

[Kayanarka]

If you read the entire original paper, problem 5 is glossed over, as I am guessing it is assumed for most of the paper that any problem 5 does not exist or has been dealt with.

 

[Randy Holmes-Farley]

If you read the entire original paper, problem 5 is glossed over, as I am guessing it is assumed for most of the paper that any problem 5 does not exist or has been dealt with.

"5. The aquarium is still cycling, and has excess acid being produced from the nitrogen cycle and degradation of organics to CO2."

The potential for that is shown by low alkalinity (the acids added lower the alkalinity). If alkalinity is not low, this is not the issue.

 

[ying yang]

Lol. I heard a story that a Reefer was able to catch a cheating spouse by monitoring pH and figuring out why his pH kept dipping while he was at work.

Ha ha from heavier panting producing more co2 from the cheating spouse doing the oke cokey i take it ^_^
So if anyone suspects the other half is cheating,instead hiring a private investigator,they can just have an aauarium with a ph probe and monitor ph levels ha ha i love it

 

[Randy Holmes-Farley]

FWIW, there are plenty of folks who have watched with dismay when the pH in their aquaria took a nosedive during a big party at the house.

 

[MnFish1]

There is nothing else besides CO2 (in the water, not the air) and carbonate alkalinity that determine pH (well, minor effects from temp and salinity). pH, alk, and CO2 in the water are related mathematically.

Thanks - that was my interpretation - and thanks for confirming it!