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Strange water parameters after switching from rainwater to RO

_Maq_

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how often do you change the carbon
I think the carbon works as a catalyst when removing chlorine, so it should be effective in this respect indefinitely. Am I wrong?
 

dino21

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I think the carbon works as a catalyst when removing chlorine, so it should be effective in this respect indefinitely. Am I wrong?
No - "Activated Carbon is also a catalyst that converts free chlorine (Hypochlorite ) to chloride which is easily adsorbed"

- though not being a chemist, no idea how long that process can be maintained by the carbon ?
The real point being , its good for the reduction of other contaminants and to protect the membrane, to change the carbon and pre filter regularly.
 

jaypeecee

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After changing the basis water from rain to RO, I observed that all my crystal shrimps have died. Cherry shrimps are also not very happy from what I see.

Hi @Vsevolod Stakhov

Could this be a copper problem? As you will be aware, shrimp are very sensitive to copper. Do you have a copper test kit just to be sure that this isn't the culprit?

JPC
 

Vsevolod Stakhov

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Ok, it seems that TDS in soil sample has stabilized at 100ppm. So I have decided to meausure main water parameters.

PH:
APC_0331.jpg
All around 7, hard to distinguish differences at that point.
RO water: KH=0..0.5, GH=0, PO4=0 - so my RO unit seems to be fine
Soil water: KH=1..1.5, GH=3(!), PO4=0

So it seems that soil leaches hardness ions. It is just a mess :(
 

Vsevolod Stakhov

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I wouldn't expect anything else.
Yes, it's likely the same parameters I have in my tank. The problem is that 1) I don't need that high PH; 2) I don't want all PO4 to be absorbed and excluded from the buffering system. And I've never seen such a behaviour with old Tropica soil. Probably it wasn't old enough though. I think I need to use RO only during water changes and add some CaCl2 for GH raise.
 

_Maq_

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I don't want all PO4 to be absorbed and excluded from the buffering system.
You could hardly prevent it from happening. Phosphates readily adsorb to metal oxides, organic matter, clays.
Clays do not act in a simple fashion. Firstly, there are many kinds of clay and each of them has different affinity for different cations. Still, even if you use a single purified clay, its behavior is influenced by the presence of various cations around, incl. protons, i.e. pH. Par example, it is possible to bath a clay in a very acidic solution and replace many metal cations by protons. Then you can pack it under the name ADA Amazonia and when it comes to hard and alkaline water, it will bind metal cations and release protons instead.
 

Vsevolod Stakhov

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Then you can pack it under the name ADA Amazonia and when it comes to hard and alkaline water, it will bind metal cations and release protons instead.
Yes, I'm aware of this process. In fact, with hard water and soil you can even reach green drop-checker due to extra protonation and absorbtion of the Ca/Mg cations (leaving HCO3- as H2CO3 basically). But it seems that my soil has no protons left, but it has some Mg/Ca and I really don't know the exact cations balance and so on. Indeed, it could be that soil has absorbed too much Cu(2+) somehow and it got suddenly emitted to water... Yes, there are free EDTA and other free chelators in that water but I'm still not convinced.
 

_Maq_

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it could be that soil has absorbed too much Cu(2+) somehow
Well, certainly a possibility.
What intrigues me is that both rainwater and RO water should be of low ionic strength, so replacing one with another should not make much of a change. Still, you lost some shrimps, and water pH behaves differently. I don't get it.
 

jaypeecee

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RO water cannot have more copper than tap water apparently.

Hi @Vsevolod Stakhov

The job of the RO membrane is to remove molecular contaminants. That's why it's preferable to follow this with a deionizer stage to remove ionic compounds. I no longer have my own RO unit. But, I always ensure that I purchase RO + DI water from my LFS. This water measures typically 5 microS/cm. Only a defective RO+DI system could possibly have copper more than tap water. The latter is permitted to have copper up to 2 mg/l.

JPC
 

Vsevolod Stakhov

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What intrigues me is that both rainwater and RO water should be of low ionic strength, so replacing one with another should not make much of a change. Still, you lost some shrimps, and water pH behaves differently. I don't get it.
Maybe rainwater -> RO change is negligible, and the culprit was the temperature rise (I normally keep this tank at around 19-20 degrees, but it got heated to 27 degrees during the recent heat). Perhaps, that temperature change could have caused some structural changes in the soil. Does it look possible?
 

_Maq_

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Does it look possible?
Good idea, I think. Temperature may influence many reactions. The problem is that the soil is a blend of myriads of substances, so one never knows for sure...
What if the released cations were ammonium? That could have killed the shrimps. To me it sounds more likely than excess copper.
 

Vsevolod Stakhov

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What if the released cations were ammonium?
Maybe, as with the conjunction of the raised PH it might be really bad. As I've said, I add half of my N as urea, that actually hydrolises to NH4+ in aqueous solution with time (and my hand made fertiliser was quite old to have all urea N as NH4 N). Normally, it is not a problem as plants absorb NH4 quickly, but this process is also not persistent: e.g. it heavily depends on lighting. So maybe higher temperature, higher PH, higher ammonia, less oxygen (due to temperature rise). That wasn't that bad for fish but crystal shrimps seem to be much more sensitive...
 
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