# Strange water parameters after switching from rainwater to RO



## Vsevolod Stakhov (20 Jul 2022)

Hello, I have some weird issues with my water in my softwater planted tank with Colombo soil. I always add around 75-80% of the rainwater and mix it with tap water (hard 110ppm Ca, 12dKH). TDS of my rain water was around 5-7ppm and TDS of the RO water is around 15ppm. TDS in the tank is around 168ppm.

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. I have measured water parameters and they are quite confusing. PH with CO2 is 6.8 but when I remove extra CO2 by shaking it raises up to 7.6, with dKH=2-3. In another planted tank that has exactly the same dKH I have PH with CO2 equal to 6 and PH without CO2 equal to 6.8 (which is totally reasonable). I'm trying to understand why do I have such a high PH now, as with rain water it was not higher than 6.

One hypothesis is that the lower PH in the large planted tank is caused by phosphates buffer, as that tank has ~2ppm of PO4 according to the API test kit. Smaller tank has 0.25ppm of PO4 (that could be explained by aquasoil).

I see no visible issues with fish and plants (R. macrandra, fissidens, monte carlo etc), but I cannot understand why I have that PH rise and what has happened with my shrimps. Any ideas are much appreciated - I can provide more information if needed.


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## jaypeecee (20 Jul 2022)

Vsevolod Stakhov said:


> Hello, I have some weird issues with my water in my softwater planted tank with Colombo soil.


Hi @Vsevolod Stakhov

I just had a very quick look around before I need to water the garden!

Is the following of any relevance to what you are reporting:









						Colombo Florabase substrate review
					






					www.practicalfishkeeping.co.uk
				




I also noted the following:

"This product looks good, feeds plants and can lower pH".

"With the potential to release ammonia this isn’t a product for beginners..."

JPC


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## Vsevolod Stakhov (20 Jul 2022)

jaypeecee said:


> "This product looks good, feeds plants and can lower pH".


Yes, but in my case PH is much higher than PH in the nearby tank with the neutral soil and the same RO system and the same dKH. I really don't understand why it can be the case (well, aside of PO4 concentration...).


jaypeecee said:


> "With the potential to release ammonia this isn’t a product for beginners..."


There are two soils: one with nutritients and one without. I have one that has no nutritients. Anyway, this tank is one year old, it was properly cycled on ammonia prior to anything, it has decent filtration and I actually use fertilizers with ammonia. So I'm not scared of ammonia, but I'm, well, scared about such an unpredicted PH rise for no apparent reason (dKH is still quite low).


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## Hufsa (20 Jul 2022)

I may be completely missing the plot here but is it possible that the switch to uber clean RO has caused something to leach out of the substrate?


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## Vsevolod Stakhov (20 Jul 2022)

Hufsa said:


> I may be completely missing the plot here but is it possible that the switch to uber clean RO has caused something to leach out of the substrate?


The TDS at the output of the RO unit is slightly higher than for rainwater butt: like 15ppm vs 7ppm. Anyway, I have slightly a different hypothesis now: when rainfall got depleted I've added some RO water directly to the water butt disturbing the long lived mud on the walls and at the bottom. Maybe there were some toxic chemicals, such as pesticides or other biocides buried in that mud? That could explain sensitive shrimps deaths but it still does not explain the higher PH comparing to the neutral substrate tank.


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## tam (21 Jul 2022)

RO water should really be <10 - ideally pretty close to 0. It might be your filters need changing. The rain could have some hardness in it (rain isn't necessarily zero everything), so rain isn't necessarily the same as RO.  How accurate is your mixing 20% tap would give you 2.4gh - which I think is a little low for shrimp? If your rain had some gh maybe that was enough to just bring it up enough for them. If you then added RO to it, you'd have reduced the gh in the rain and ended up with a lower gh.

What's your gh in the tank? The TDS reading might seem fine, but it may be made up of all sorts of 'stuff' that isn't gh. In fact your tank TDS seems very high if you are using 80% RO/rain.


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## Vsevolod Stakhov (21 Jul 2022)

tam said:


> RO water should really be <10 - ideally pretty close to 0.


TDS meters actually measure conductivity, not the real TDS. Hence, even dissocated CO2 (as H+ and HCO3- ions) influence on those readings. So I'm not really blaming my RO membrane.


tam said:


> How accurate is your mixing 20% tap would give you 2.4gh - which I think is a little low for shrimp?


My tap water has 12dKH and 18-19dGH + I also add some MgSO4 (to 5ppm Mg) during water preparation. So dGH is around 5, which is totally fine for shrimps I suppose.


tam said:


> In fact your tank TDS seems very high if you are using 80% RO/rain.


It's probably because of EI like fertilization mode and CO2 injection. It has always been around this value.

One thing I really don't understand is the PH difference with a tank that has neutral substrate (that also uses the same RO water + tap water mix). Soil tank PH must be lower and it was lower in the past. So why could it change, counting that KH is the same?


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## Vsevolod Stakhov (21 Jul 2022)

Plants and snails also look fine, that's just shrimps that were affected:


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## _Maq_ (21 Jul 2022)

Vsevolod Stakhov said:


> TDS meters actually measure conductivity


Yes, and I find it quite surprising that TDS measurements appear in this forum quite often. TDS meters do measure conductivity and transform the number to TDS by using some factor chosen quite liberally. In the end, it says pretty nothing.
(I'm intrigued by your problem but have no ideas, suggestions. It's really weird. Could it be that, p.e. after long period of inactivity, your RO machine got somehow "bad"?


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## Vsevolod Stakhov (21 Jul 2022)

Ok, I have started a simple expreiment: I've added soil to a small container, washed it with RO water and filled the container again with RO water. I have used another container as a reference:



Initially my reference sample has TDS=28, so it seems that my RO membrane needs to be replaced, but it also depends on the source water temperature (it is hot now) and the source pressure (the pressure is low). The sample with soil behaves differently. Initially TDS was equal to 33, in one hour it was 42 and after another hour it was 55. So something definitely leaches from the soil. I will wait for some more time unless tds stops changing and try to check kh/gh/ph...


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## Vsevolod Stakhov (22 Jul 2022)

Vsevolod Stakhov said:


> I will wait for some more time unless tds stops changing


95ppm today  That's really worrying.


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## _Maq_ (22 Jul 2022)

Vsevolod Stakhov said:


> That's really worrying.


Yet not that surprising, at least to me.
Still, if I'm not mistaken, the soil remains the same. It's the water which turned from rain to RO. I'd suppose both should react with the soil in similar fashion. Perhaps exchanging protons for some metal cations at cation exchange sites of the clay which forms a part of the soil. I'm still short of ideas what made such a striking difference.
Have you checked for all possible flaws, like invalid measurements, defect RO machine, etc.?


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## dw1305 (22 Jul 2022)

Hi all, 


_Maq_ said:


> Yes, and I find it quite surprising that TDS measurements appear in this forum quite often. TDS meters do measure conductivity and transform the number to TDS by using some factor chosen quite liberally. In the end, it says pretty nothing.


This has come up a <"few times on the forum"> and <"conductivity in microS"> is a much more  sensible unit. 

I think the problem is a bit like using "dGH" and "dKH". The aquarium industry uses them, and "ppm TDS" etc., even though they <"are bizarre derived units"> and microS and mg / L would make a lot more sense.

cheers Darrel


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## John q (22 Jul 2022)

Vsevolod Stakhov said:


> 95ppm today  That's really worrying.


Have you tried the same experiment with rain water?


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## tam (22 Jul 2022)

Is that existing substrate taken out of your tank or new out of a bag? I'd expect it to produce less after its been in a tank awhile.

Also, are you dechlorinating still - you don't know what's coming through your RO if you are getting high tds?


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## Vsevolod Stakhov (22 Jul 2022)

_Maq_ said:


> Perhaps exchanging protons for some metal cations at cation exchange sites of the clay which forms a part of the soil.


The RO water has not many free H+ cations (1*10-7 in molar concentrations). Dissolved CO2 gives some but not many. But if soil exchanges protons with, let's say, K+, then PH raise is clearly here. But I was under impression that the soil should do the opposite exchange or it is kinda... useless.


_Maq_ said:


> It's the water which turned from rain to RO.


It might be a coincidence and unrelated thing. Shrimps could die because of something washed out from the rainwater butt and PH could just gradually increase over time (I've not measured it constantly tbh).


John q said:


> Have you tried the same experiment with rain water?


I have some small amounts of rainwater left. But it is duluted with RO water and it has TDS=25 due to heavy evaporation 


tam said:


> s that existing substrate taken out of your tank or new out of a bag


It is the the existing substrate washed in RO water initially to remove dirt and mug.


tam said:


> Also, are you dechlorinating still


It seems to be useless for RO as there is a carbon filter before RO membrane. Also, free chlorine in form of ClO ions affects conductivity, so it is not possible to have any decent amount of those ions with that TDS readings. Chloramine, on the contrary, has likely no chances to pass RO membrane due to it's molecule size.


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## John q (22 Jul 2022)

Vsevolod Stakhov said:


> is duluted with RO water and it has TDS=25 due to heavy evaporation


I suspect that the ro unit is somehow adding kh?  surely that's the only explanation?  I think the substrate is a red herring on this occasion. Hence the need for testing with rain water.


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## John q (22 Jul 2022)

Vsevolod Stakhov said:


> Also, free chlorine in form of ClO ions affects conductivity, so it is not possible to have any decent amount of those ions with that TDS readings.


1ppm of free chlorine will kill your fish...  tds goes from 152 to 153.... is that leaf melt, saliva thats dribbling from your chin or chlorine...


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## Vsevolod Stakhov (23 Jul 2022)

John q said:


> I suspect that the ro unit is somehow adding kh?


Hold on, RO unit apparently skips some HCO3 ions and it has non zero KH. But you cannot find a single dKH in RO water using aquarium tests (that are very precise btw) - I've tested it many times. So my quality check of an RO unit is simple: if KH probe is red from the first drop, then RO unit works (of course, it is true merely for my hard tap water). So the final dKH of RO unit is <1. Otherwise, it is a clear sign that you need to replace membrane.


John q said:


> 1ppm of free chlorine will kill your fish


I have no doubts that 1ppm of free chlorine will kill fish and shrimps. I've even tested that on my daphnia cultures (those cultures could survive 60ppm of total NH3+NH4 at PH=8, but 1ppm of free chlorine has killed all of them in 48 hours). However, my tap water has around 0.1ppm of free chlorine and RO unit will filter at least 90% according to PPM and the ionic radius of the HClO (it is not B!). So I'd exclude free chlorine here...

The only parameter that I cannot understand is PH: why PH on a soil based tank is higher than on a neutral substrate with the same dKH. And this PH difference cannot be explained by CO2 levels difference, as I have shaked samples for quite a long to ensure that CO2 is in equilibrium with the atmosphere.


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## dino21 (23 Jul 2022)

A basic RO system will not produce 0 tds in a hard water area as its only about 95-99% effective.
In such cases you need a add, if not already fitted, a fourth pod using a DI resin to remove those last traces.
If you do have DI fitted it may be just a case of renewing or 'cleaning' the resin,
How old is the RO membrane and how much water are you running though it a week ?
Do you have and use a flush kit on it, before each session ?
Chlorine should be removed by the Carbon filter as it can damage the RO membrane,  again how often do you change the carbon  and the pre filters ?


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## _Maq_ (23 Jul 2022)

dino21 said:


> 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?


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## dino21 (23 Jul 2022)

_Maq_ said:


> 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.


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## jaypeecee (23 Jul 2022)

Vsevolod Stakhov said:


> 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


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## Vsevolod Stakhov (23 Jul 2022)

jaypeecee said:


> Could this be a copper problem? As you will be aware, shrimp are very sensitive to copper.


No, I don't think so. I had cherry shrimps for ages on tap water with no issues. RO water cannot have more copper than tap water apparently.


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## Vsevolod Stakhov (23 Jul 2022)

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

PH:




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


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## _Maq_ (23 Jul 2022)

Vsevolod Stakhov said:


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


I wouldn't expect anything else.


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## Vsevolod Stakhov (23 Jul 2022)

_Maq_ said:


> 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.


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## _Maq_ (23 Jul 2022)

Vsevolod Stakhov said:


> 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.


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## Vsevolod Stakhov (23 Jul 2022)

_Maq_ said:


> 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.


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## _Maq_ (23 Jul 2022)

Vsevolod Stakhov said:


> 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.


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## jaypeecee (23 Jul 2022)

Vsevolod Stakhov said:


> 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


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## Vsevolod Stakhov (23 Jul 2022)

_Maq_ said:


> 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?


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## _Maq_ (23 Jul 2022)

Vsevolod Stakhov said:


> 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.


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## Vsevolod Stakhov (23 Jul 2022)

_Maq_ said:


> 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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