Edward

Hi,
is there a procedure, that can determine CO2 concentration in water at zero degree KH? The pH => KH table doesn't do it here.

My tanks have no issues with algae. Plants look great and fish are happy. Lemon Tetra (Hyphessobrycon Pulchripinnis) is breeding and raising fry without my intervention. The only problem I have is to control the CO2 level.

Details:

Black Neon Tetra
Bleeding Heart Tetra
Lemon Tetra
Cardinal Tetra

Hemianthus Callitrichoides
Glossostigma Elatinoides
Limnophilla Aromatica
Ludwigia Inclinata
Hydrocotyle Verticillata
Rotala Wallichii
Ludwigia Arcurata
Didiplis Diandra
Rotala Rotundifolia
Ludwigia Repens

RO water only

pH 4.1 - 5.2
TDS 150 - 250 uS
KH 0
NO3 5 - 20 ppm
PO4 0.25 - 1.00 ppm
K 10 ppm estimated
Ca2 10 - 20 ppm
Mg2 2.5 - 5.0 ppm
Fe TE (when Ludwigia Repens needs it)

K2SO4
KNO3
KH2PO4
MgSO4
TE (Fe EDTA 5%, Fe DTPA 2%, Mn 2%, Zn 0.4%, Cu 0.1%, B 1.3%, Mo 0.06%)

Mix of ratio
3.0 g CaSO4
1.0 g CaCl
1.5 g Soda
1.0 g MgSO4

It would be much easier if I could determine the CO2 concentration and keep it at 20 - 30 ppm.
Thank you,
Edward

plantbrain

Well no, you will not be able to determine at a KH of 0. pH test probes will also not work on pure water. You have some salts but no HCO3.

HCO3/CO2 is an acid base buffered system. Without the base, there's no pH/KH relationship.

The system will crash, it might not have done this yet for you, but you'll get burned at some point. And have dead fish.

My question to you is this: why do use RO water with no KH added back?
Bring it up to 2 at least.

Do this for your fish and for your plants. It will help and cause no issues with any fish or plants you mention or anyone's mentioned, even wild Rio Negro Discus, Altums etc do fine at a KH of 3.

Plants will use KH if there is not enough CO2 also. You may be hitting the right amount of CO2 for now, but that may not last long. If the plants do not have enough CO2 at some point, then the pH wioll rise dramatically since there's no base to balance it. Our blood has the same acid base system and is why we exhale CO2 as we oxidize the sugars we eat for energy.

Think about the acid base system, if you add a lot of acid and there's no base to balance it, then you can have very large pH fluctations. Potentially lethal to fish also.

Add some baking soda and raise the KH to 2-3 range, then add enough CO2 to get about 6.3-6.5 range.

All the fish will and can breed in this range.
Food and feeding will help the most in general with most breeding issues.

This will take care opf both fish and plants.
In general, taking care of the plants takes good care of the fish, the rest is mainly feeding.

Regards,
Tom Barr

Edward

Tom,
let me Thank you for the great help you have done for the aquatic plant community. Most of us would be still fighting algae today.


What condition is considered as a harmful pH crash is difficult to determine. In some parts of South American rivers water level rises several meters after rain fall. This water is filled with humid acid and CO2 from plant decomposition. Conductivity remains as low as 10 uS, pH around 5 and KH only in traces.

This is the environment where fish and plants flourish. For example Cardinal Tetra larvae will not develop and die in KH over 0.2 ppm, GH other then 1-2, pH over 6.0 (ideal 5.5) and conductivity other then 10-30 uS. So why not give plants and fish such conditions when RO allows it.

I've been keeping plants and fish in pH of 4.0 to 5.0 for the last 3 years with no problems. Some Tetras breed and raise babies and that is a prove how healthy environment they have. Most Tetras wouldn't be able to develop in KH of 2.

I have tried to increase KH with soda some time ago, but it was never ending struggle. Unstable pH fluctuations made it difficult. If there is a stable KH source like tap water then water changes don't cause variations. In my tanks with zero KH the pH fluctuation is 0.4 pH at most. Not much different then tanks with KH of 3. What mechanism is making the pH so stable without the KH buffering?

I believe that we are unnecessarily obsessed with the pH issue. The need to keep it in the range of 6.9-7.1 is a myth.

Thank you,
Edward

gpodio

I agree with Tom's suggestion, I would raise the KH above 0.

But there is a post at the end of this page that suggests a different equation to measure CO2 levels that doesn't use KH as reference. Perhaps it may work for you, but says you will need to have very precise PH readings:

http://www.thekrib.com/Plants/CO2/kh-ph-co2-chart.html

Hope that helps
Giancarlo Podio

fishfry

I have always used straight R/O for my South American fishes. My rams have bred over and over, and now in my plant tank my toninas just love the KH ~1
to each their own I guess...?

tsunami

But Tonina's don't need such soft water to grow well. Tonina fluviatilis grows just fine in KH 4, GH 5 water:



Plus, many plants like Ammania gracilis and Nesaea pedicellata seem to prefer the slightly harder water. Plants do need calcium and magnesium, after all.

Carlos

Edward

gpodio

Thanks for the shortcut. I followed the article http://www.thekrib.com/Plants/CO2/kh-ph-co2-chart.html and have done few experiments to realize later that the equation is probably wrong.

log(CO2) = pH(a) - pH(t) - 0.3

example 1
pH(a) 8, pH(t) 7, takes 5 ppm CO2

example 2
pH(a) 7, pH(t) 6, takes 5 ppm CO2

It is clear that this is wrong. From CO2/KH/pH chart http://www.eheim.com/technik_co2_dauertest.htm we can see it takes 10x more CO2 at 6 pH then at 7 pH.

I am hoping to find more options to measure CO2 levels.

Thank you,
Edward

Edward

tsunami

we don't use soft water because plants need it, but because it is more convenient when RO is used.

Controlling stable level of KH with chemicals is not easy task. Too many variables, too much time and work. So why not let the water stabilize naturally on it's own. I tried and it seems to be working just fine.

Yes, plants need Calcium and Magnesium. When Calcium test kit reads bellow 20 ppm Ca2, I dose CaCl, CaSO4, Soda and MgSO4 premixed dry in the right ratio Ca:Mg:Na.

Thank you,
Edward

fishfry

doesn't Flourish contain all the essential minerals that R/O takes out of the water?

gpodio

No Flourish is more of a generic all-round fertilizer/trace mixture made to suit many different tanks. Equilibrium is Seachem's product for RO water, and you will need to still raise KH and this only effect GH and some other elements not associated with water hardness.

Giancarlo Podio