The Planted Tank Forum banner
41 - 60 of 173 Posts

·
Registered
Joined
·
3,037 Posts
There are several factors involved with this so called pH crash which I actually attribute to C02
poisoning or oxygen depletion.

To try and help the general understanding of what I know of what is going on in the water of
these acidic tanks, streams and rivers I will copy and paste some information I have found viable
in growing weeds and fish in acidic condition's.

Biochemical Oxygen Demand, or BOD, is a measure of the quantity of oxygen consumed by
microorganisms during the decomposition of organic matter. BOD is the most commonly used
parameter for determining the oxygen demand on the receiving water of a municipal or industrial
discharge. BOD can also be used to evaluate the efficiency of treatment processes, and is an
indirect measure of biodegradable organic compounds in water.

Imagine a leaf falling into a stream. The leaf, which is composed of organic matter, is readily
degraded by a variety of microorganisms inhabiting the stream. Aerobic (oxygen requiring)
bacteria and fungi use oxygen as they break down the components of the leaf into simpler, more
stable end products such as carbon dioxide, water, phosphate and nitrate. As oxygen is
consumed by the organisms, the level of dissolved oxygen in the stream begins to decrease
Water can hold only a limited supply of dissolved oxygen and it comes from only two sourcesdiffusion
from the atmosphere at the air/water interface, and as a byproduct of photosynthesis.
Photosynthetic organisms, such as plants and algae, produce oxygen when there is a sufficient
light source. During times of insufficient light, these same organisms consume oxygen. These
organisms are responsible for the diurnal (daily) cycle of dissolved oxygen levels in lakes and
streams.

If elevated levels of BOD lower the concentration of dissolved oxygen in a water body, there is a
potential for profound effects on the water body itself, and the resident aquatic life. When the
dissolved oxygen concentration falls below 5 milligrams per liter (mg/l), species intolerant of low
oxygen levels become stressed. The lower the oxygen concentration, the greater the stress.
Eventually, species sensitive to low dissolved oxygen levels are replaced by species that are
more tolerant of adverse conditions, significantly reducing the diversity of aquatic life in a given
body of water. If dissolved oxygen levels fall below 2 mg/l for more than even a few hours, fish
kills can result. At levels below 1 mg/l, anaerobic bacteria (which live in habitats devoid of
oxygen) replace the aerobic bacteria. As the anaerobic bacteria break down organic matter,
foulsmelling hydrogen sulfide can be produced.

BOD is typically divided into two parts- carbonaceous oxygen demand and nitrogenous oxygen
demand. Carbonaceous biochemical oxygen demand (CBOD) is the result of the breakdown of
organic molecules such a cellulose and sugars into carbon dioxide and water. Nitrogenous
oxygen demand is the result of the breakdown of proteins. Proteins contain sugars linked to
nitrogen. After the nitrogen is "broken off" a sugar molecule, it is usually in the form of ammonia,
which is readily converted to nitrate in the environment. The conversion of ammonia to nitrate
requires more than four times the amount of oxygen as the conversion of an equal amount of
sugar to carbon dioxide and water.

When nutrients such as nitrate and phosphate are released into the water, growth of aquatic
plants is stimulated. Eventually, the increase in plant growth leads to an increase in plant decay
and a greater "swing" in the diurnal dissolved oxygen level. The result is an increase in microbial
populations, higher levels of BOD, and increased oxygen demand from the photosynthetic
organisms during the dark hours. This results in a reduction in dissolved oxygen concentrations,
especially during the early morning hours just before dawn.
In addition to natural sources of BOD, such as leaf fall from vegetation near the water's edge,
aquatic plants, and drainage from organically rich areas like swamps and bogs, there are also
anthropogenic (human) sources of organic matter. If these sources have identifiable points of
discharge, they are called point sources. The major point sources, which may contribute high
levels of BOD, include wastewater treatment facilities, pulp and paper mills, and meat and food
processing plants.

Organic matter also comes from sources that are not easily identifiable, known as nonpoint
sources. Typical nonpoint sources include agricultural runoff, urban runoff, and livestock
operations. Both point and nonpoint sources can contribute significantly to the oxygen demand in
a lake or stream if not properly regulated and controlled.

Performing the test for BOD requires significant time and commitment for preparation and
analysis. The entire process requires five days, with data collection and evaluation occurring on
the last day. Samples are initially seeded with microorganisms and saturated with oxygen (Some
samples, such as those from sanitary wastewater treatment plants, contain natural populations of
microorganisms and do not need to be seeded.). The sample is placed in an environment suitable
for bacterial growth (an incubator at 20o Celsius with no light source to eliminate the possibility of
photosynthesis). Conditions are designed so that oxygen will be consumed by the
microorganisms. Quality controls, standards and dilutions are also run to test for accuracy and
precision. The difference in initial DO readings (prior to incubation) and final DO readings (after 5
days of incubation) is used to determine the initial BOD concentration of the sample. This is
referred to as a BOD5 measurement. Similarly, carbonaceous biochemical oxygen test
performed using a 5-day incubation is referred to as a CBOD5 test.
http://www.deq.state.mi.us/documents/deq-swq-npdes-BiochemicalOxygenDemand.pdf

Fish waste, excess food and even filter media play a vital role in the success or failure of this
environment. But ultimately it is the lack of oxygen that kills fauna, very high levels of C02 can do
this also obviously, but with high levels of C02 you also get lower levels of oxygen, so the proper
amount of surface agitation is vital.

High quality filter and media plays a vital role in this environment also because it helps control
nitrate, nitrite and ammonia..nitrate is also a form of acid, nitric acid.

BIOLOGICAL FILTRATION

It is no exaggeration to say that the condition of an aquarium depends very much on the performance
of its biological filter. When the filter's micro-organisms are thriving, the water will be crystal
clear and there is no algae growth.

The chemical reaction that expresses the oxidation process carried out by the nitrobacteria which
converts harmful ammonia into harmless nitrate is NH3; NO2; NO3. The bacteria that converts ammonia
(NH3) into nitrite (NO2) is called Nitrosomonas, and the bacteria that converts that into nitrate
(NO3) is called Nitrobactor. Research shown that the remaining nitrate is about 70 times less toxic
than nitrite, but if enough accumulates in the water it canstill be harmful. Therefore, it is always
necessary to frequently change the aquarium water even when using a top-of-the-line filter.

So we need good filters and media, lots of oxygen or surface agitation, but not to the degree that we
degrade our level of C02 content....which will be evident by algae growth, fish gasping and or poor
plant health based on the amount of light over the tank, and keeping the tank clean and free from excess
organic's, dead floating, rotting plant matter, and frequent water change's.

It is an environmental thing.
 

·
Registered
Joined
·
2,783 Posts
fresh_newby said:
Coke is not highly acidic just becuse of CO2...It has acid as an ingredient in addition to carbonation <CO2>. Release of CO2 makes it more basic. Our tanks are not under the same pressure as Coke is, nor anything that is carbonated and remains carbonated. This is not a good conparitor. Coke is not a result of a pH "crash" At steady state Coke is at 4 tops, I would surmise.
All the buffering does is slows the delta so it has less absorption capacity. It is less forgiving without said buffer, but it does not mean that it is unstable, just less stable.

Active ingredient...phosphoric acid......very powerful...coke will dissolve a steak in 3 days......I did it for a school cience project.....
 

·
Registered
Joined
·
764 Posts
I myself wouldn't be so worried about the low pH level than of the possible fluctuations of pH during the day. At least in Walstadt's book she describes how plants' photosynthesis and the consumed CO2 can up the pH a lot when there the alkalinity is low. Maybe this is not a problem with the high tech tanks and CO2 injection with pH controller but what about DIY systems and such? No problem?

Quoting from the book (p. 92):
"At an acidic pH of 5 and below, most of the water's [dissolved inorganic carbon] is CO2. At pH 6.5 the water contains about equal amounts of CO2 and bicarbonate, while at ph 8.5, almost allof the CO2 has converted to bicarbonates."
 

·
Registered
Joined
·
3,254 Posts
mrbelvedere said:
Active ingredient...phosphoric acid......very powerful...coke will dissolve a steak in 3 days......I did it for a school cience project.....
Yes I clean my battery with it...That is my point. It is not the CO2 causing its highly acidic pH, it is added acid. So Coke is not a good representation of a "pH crash" which was the argument made. Just because it is carbonted doesn't mean it can be used as a comparitor.
 

·
Registered
Joined
·
879 Posts
Wö£fëñxXx said:
I hope this helps all, at least some with their acidic endeavor's :biggrin:
I have enjoyed reading the response of all that have post so far, let it continue that we may grow in knowledge :thumbsup:

Yah it helped. Thank you.
I looked to co2 to get my low pH habitat regardless of kh or gh, which are also on the low end of the scale. co2 is what led me to the planted tank.

So the debate here is that co2 will crash the pH in a 0-2KH environment?
Sorry for being a little slow.
Or is it that the lower the KH the lower the co2 you need to inject?

If pressurized co2 and 0-2 KH means pH crash exactly how long is this going to take? Ive been running for at least 3 months like this.

More questions...since my KH is nil and low GH does my Milwaukee pH51 handheld pH meter even work? accurate? I calibrate it often...does this even matter?
 

·
Registered
Joined
·
3,199 Posts
Discussion Starter · #46 ·
Anyone who has recieved Craig's plants (Wolfenxex...I don't know how you type that) via trade has seen some of the healthiest plants that can be grown. Now I can't seem to dose EI with success, perhaps because I have too heavily stocked tanks. But, the proof is in the pudding - if you have seen his plants - that perhaps this low KH option is the real deal. I'm hoping that we do not need to approach 5 pHs to get there, just low KH levels around 2-3 dKH...

And Brilliant, I believe you do need to dose some baking soda to get any reading on your pH meter. At least 1 dKH. At least the APC thread suggested that. And you may need to dose a little for GH too.
 

·
Registered
Joined
·
1,666 Posts
I was worried about including coke as there are a lot of other things as mentioned. This is why I like the particular chart I posted as it includes other sodas but you are right that there are other non sodas at low pH... So lets compare to "club soda."

Buffers are best at +-1 pH unit from the pKa (~6.3) so when you push below 5.3 or so the pH changes much more rapidly. I think this is covered in the post that suggests that you don't set and forget.

Also the species as a function of pH changes as posted earlier as CO2 as the easy to draw form is a Diprotic Acid.
http://curvebank.calstatela.edu/acid_base/acid_base.htm

So I guess I am trying to say that low KH tanks with aggressive CO2 dosing has some finite risk or collapse due to inattention or hardware malfunction. However there are many places where this occurs in the wild so read the fish and plants. I am also on the same soft PNW water as Betowess so I guess I should just enjoy it.

fresh_newby said:
Coke is not highly acidic just becuse of CO2...It has acid as an ingredient in addition to carbonation <CO2>. Release of CO2 makes it more basic. Our tanks are not under the same pressure as Coke is, nor anything that is carbonated and remains carbonated. This is not a good conparitor. Coke is not a result of a pH "crash" At steady state Coke is at 4 tops, I would surmise.
All the buffering does is slows the delta so it has less absorption capacity. It is less forgiving without said buffer, but it does not mean that it is unstable, just less stable.
 

·
Registered
Joined
·
3,254 Posts
We agree on that, hence me saying that it is much less forgiving at these levels, so attention is def. required. There is small room for error so to speak. I am stil at kH of about 1.5 and my pH is holding steady at 6.3. No problems to report as of yet, knock on wood.


BlueRam said:
I was worried about including coke as there are a lot of other things as mentioned. This is why I like the particular chart I posted as it includes other sodas but you are right that there are other non sodas at low pH... So lets compare to "club soda."

Buffers are best at +-1 pH unit from the pKa (~6.3) so when you push below 5.3 or so the pH changes much more rapidly. I think this is covered in the post that suggests that you don't set and forget.

Also the species as a function of pH changes as posted earlier as CO2 as the easy to draw form is a Diprotic Acid.
http://curvebank.calstatela.edu/acid_base/acid_base.htm

So I guess I am trying to say that low KH tanks with aggressive CO2 dosing has some finite risk or collapse due to inattention or hardware malfunction. However there are many places where this occurs in the wild so read the fish and plants. I am also on the same soft PNW water as Betowess so I guess I should just enjoy it.
 

·
Registered
Joined
·
3,254 Posts
Betowess said:
Anyone who has recieved Craig's plants (Wolfenxex...I don't know how you type that) via trade has seen some of the healthiest plants that can be grown. Now I can't seem to dose EI with success, perhaps because I have too heavily stocked tanks. But, the proof is in the pudding - if you have seen his plants - that perhaps this low KH option is the real deal. I'm hoping that we do not need to approach 5 pHs to get there, just low KH levels around 2-3 dKH...

And Brilliant, I believe you do need to dose some baking soda to get any reading on your pH meter. At least 1 dKH. At least the APC thread suggested that. And you may need to dose a little for GH too.
Craig's plants are very healty. I can attest to that!
 

·
Registered
Joined
·
1,666 Posts

·
Registered
Joined
·
879 Posts
BlueRam said:
A prior thread (with pictures!) discussing CO2 and pH in crash like situations.
http://www.plantedtank.net/forums/g...bility-experiment-photos-video-evidence.html?

Can you point out where?

The author mentions this having nothing to do with pH. I just spent the last half hour reading that co2 disolves in water quickly.

The answer to the thread would be YES, you can add co2 with no or low KH without a crash. Unless your considering the fact that the pH reading goes lower when co2 is added is a "crash".

Then there is that whole..."add plenty of everything" attitude....which doesnt exactly work with this low KH water....which I am assuming is the whole issue here.
 

·
Registered
Joined
·
3,254 Posts
lol well at least now I remember the Henderson-Hasselbalch equation...lol
No mention of pH
 

·
Registered
Joined
·
635 Posts
As I was looking for something else, I ran across a few tidbits in "The Science of Fish Health Management" I thought would be of interest in this thread.

(crudely paraphrased because I don't have much patience for typing)

In acidic water, ammonia presents primarily as ammonium which is nontoxic. In alkaline ph ammonia converts to toxic ammonia which causes gill damage.

Freshwater fish can survive in extremes from 3.8 to 9.0. Fish can tolerate rapid changes in ph between 6.0 and 9.0 provided no ammonia or other toxins are present. Most fish will show some distress at ph levels between 4 and 5. Fish kept in low ph water show damage to the gill epithelium. Nitrification is reduced at ph below 5.5--ammonium quits breaking down.

The author maintains that excessive water changes can reduce the vitality of some plants and other plants do poorly under autotrophic conditions and get a boost from water changes. They suggested 20-30% every 7-14 days for fish tanks and 10-20 every two weeks for plant tanks.

Factors affecting ph include number of fish, level of organics, nitrification, and buffering capacity of the water. They state that baking soda is an adjuster rather than a buffer and that changes in ph may not hold.

It's a 14 year old book, so take it for what it's worth.

Edit: Today's trivia--Salt water fish drink water. Fresh water fish don't.
 

·
Registered
Joined
·
3,254 Posts
observant_imp said:
As I was looking for something else, I ran across a few tidbits in "The Science of Fish Health Management" I thought would be of interest in this thread.

(crudely paraphrased because I don't have much patience for typing)

In acidic water, ammonia presents primarily as ammonium which is nontoxic. In alkaline ph ammonia converts to toxic ammonia which causes gill damage.

Freshwater fish can survive in extremes from 3.8 to 9.0. Fish can tolerate rapid changes in ph between 6.0 and 9.0 provided no ammonia or other toxins are present. Most fish will show some distress at ph levels between 4 and 5. Fish kept in low ph water show damage to the gill epithelium. Nitrification is reduced at ph below 5.5--ammonium quits breaking down.

The author maintains that excessive water changes can reduce the vitality of some plants and other plants do poorly under autotrophic conditions and get a boost from water changes. They suggested 20-30% every 7-14 days for fish tanks and 10-20 every two weeks for plant tanks.

Factors affecting ph include number of fish, level of organics, nitrification, and buffering capacity of the water. They state that baking soda is an adjuster rather than a buffer and that changes in ph may not hold.

It's a 14 year old book, so take it for what it's worth.

Edit: Today's trivia--Salt water fish drink water. Fresh water fish don't.
Thanks Cheryl
Of course this book didn't take into account all of the heavy ferts in the tank that need large weekly changes. Even when I go to my LFS, they say oh no you change too much of your water way too often. They realy do not understand the differences when you have a heavily planted tank with special lihgting, and dry chemicals...etc. When I told one of the guys I was going to have fish in my tank when I cycle, he flipped out.

This is why forums such as this are so important. You have to share the experiences you have in order to come to conclusions on how to approach something that has been altered so much, such as planted tanks versus w glass box with a plastic scuba diver in it, colored rocks and buried treassure.

Anyway my 2c
 

·
Registered
Joined
·
3,199 Posts
Discussion Starter · #55 ·
Of course there are other methods like the PPS which advocate fewer ferts and much smaller water changes unless one is "resetting" the tank. I think folks grow plants successfully in both. I for one am not convinced that huge water changes are that necessary, unless dosing to excess ala EI.

BTW, interesting stuff Cheryl. And that has me wondering. The plants will take up all the ammonia as their nutrient of first choice, so the low pH should not effect that. But if the nitrification stops at pH 5.5, well, that is alarming and I wonder if that is really true. But if it is true, it might be a reason to not go much below ~ pH 6.0.
 

·
Registered
Joined
·
635 Posts
It was the ph where nitrification stopped that had me pulling the book off the shelf. I'd remembered that it stopped at a certain point and that ammonia was non-toxic in acidic waters, but couldn't remember what the ph was.

I'm one of those people who does 10-30% every week or so unless I want to shock the tank a little. I use RO/DI and can't see pouring half of it down the drain each week.

It is an older book (what the heck, I'm an older person). It isn't Moe, but is also isn't anywhere close to Fishies for Beginners. The book addresses plants throughout the chapter on water quality and has a section on plant tanks. I like more light than it suggests, but otherwise it goes along pretty well with what I've settled into over the years.
 

·
Registered
Joined
·
13,609 Posts
The whole nitrification issue is not much of one if the plants are provided for since they circumvent the NH4=> NO2=> NO3 bacterial cycle.

If you do not have actively growing plants.......say not enough CO2, limited by other things, etc, well.......then you will have issues.

A KH one 1 is plenty of get measurements and is a fairly long way off from getting down to the 0 KH range. There is always a little KH, how much is outside the range of the test kits folks use. But you can get low enough to get rapid pH changes with just a little acid or you can add small amounts of strong acids to remove nearly all the KH.

But more practical considerations come into play here: when changing water, most that have soft water, do not soften it further, nor do folks with harder water need to add reconsituted chemicals to their RO water, they simple blend 1-2 degrees of KH/Gh back into the water and then they do not need to make more RO water for a water change.

CO2 is less souble in softer water with less KH............some it will persist longer as a gas, CO2 [g] rather than as CO2[aq].


gards,
Tom Barr
 

·
Registered
Joined
·
220 Posts
I think he means that the PLANTS use up those elements. Ammonia, nitrite,and nitrate...these are taken up by the plants themselves, thus destroying the nitrogen cycle. In a tank with no plants the nitrogen cycle is important...it helps to establish the beneficial bateria in the bio filter, and the cycle in it's self can be harmful to the fish. But in a planted tank...if done properly...you will not have that exact same cycle so to speak. The plants will start to absorb the nutrients...ammonia, nitrite, or nitrate...thus breaking the cycle. That's why in a planted tank it's not nessicary to wait to put fish in. I guess technically (and according to REX and his guide) you can add all the elements from the start. start with the water...and filter, make sure you have enough light, substrate, proper ferts, and then add the plants and fish all at once...and wallah! The plants are teh bio filter and the ecosystem works well enough from the start to not be stressful for the inhabitants.
But I'd bet that Tom has a really quick answer that will clear up any dought. i'm not that quick though.
 

·
Registered
Joined
·
3,199 Posts
Discussion Starter · #59 ·
daveonbass said:
I think he means that the PLANTS use up those elements. Ammonia, nitrite,and nitrate...these are taken up by the plants themselves, thus destroying the nitrogen cycle. In a tank with no plants the nitrogen cycle is important...it helps to establish the beneficial bateria in the bio filter, and the cycle in it's self can be harmful to the fish. But in a planted tank...if done properly...you will not have that exact same cycle so to speak. The plants will start to absorb the nutrients...ammonia, nitrite, or nitrate...thus breaking the cycle. That's why in a planted tank it's not nessicary to wait to put fish in. I guess technically (and according to REX and his guide) you can add all the elements from the start. start with the water...and filter, make sure you have enough light, substrate, proper ferts, and then add the plants and fish all at once...and wallah! The plants are teh bio filter and the ecosystem works well enough from the start to not be stressful for the inhabitants.
But I'd bet that Tom has a really quick answer that will clear up any dought. i'm not that quick though.
Well, one correction on wording. The plants "circumvent" the nitrification cycle, not "destroying" the cycle, but the essence of your understanding is correct. But one still needs that bactrium cycle in the substrate, glass, filters etc. for a healthy tank.
 

·
Registered
Joined
·
635 Posts
Interesting--I had no idea that kh had an impact of CO2 solubility. Does impact oxygen levels as well?

While I'm at it, I know there's less disolved oxygen at higher temps. Does that the solubility of all gasses (i.e. less CO2 when the temps are up)?
 
41 - 60 of 173 Posts
Top