# Hypoxic fish but only after the waterchange?



## Cat (6 Sep 2020)

Hello, 
Not sure this is the appropriate section to post this but I have a group of 5 pretty small angelfish (about an inch wide) and I saw they were all gasping at the surface at around 8.30 in the evening. I've only had them about 5 days, the 24 Green neon were fine swimming about. It is a 425ish litre tank with fire extinguisher CO2 setup. I have had moments like this in the past with my discus fish again only after a water change which I do weekly at about 50% does anyone know why this would happen?

I change a few inches of water out and they all recover but obviously it's distressing for me and the fish.

Any advice would gratefully received!


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## Zeus. (6 Sep 2020)

When you do a WC the tap water already has quite a bit of dissolved CO2, so if your CO2 comes on shortly after a WC you will get a bigger pH drop and higher [CO2] hence gasping fish. 
So either let your water fully degas after WC or shorten CO2 pre lights on time should resolve the issue.
Out of interest what colour does your DC normally change and what colour on WC day?


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## GHNelson (6 Sep 2020)

Hi
There are a few theories on fish reacting badly to large water changes!

The new fish purchased from the local fish store may not be acclimatised to their new environment yet. 
There is a lot of compressed Co2 in tap water which could increase the dissolved Co2 in the aquarium to an uncomfortable level for the fish...especially the newer occupants.

Osmoregulatory stress is another avenue where fish can be affected by sudden changes in the composition of the water.
hoggie


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## alto (6 Sep 2020)

Cat said:


> I change a few inches of water out and they all recover but obviously it's distressing for me and the fish.


This seems unusual , I’ve kept angel fish in the past and they were completely fine even with 80% water changes - and my tap has significant amounts of dissolved CO2

When you introduce new fish, it does take a couple weeks for them to adjust (biochemically) to the CO2 levels often used in planted tanks (especially when this level is 30ppm (and higher) vs 10-15ppm)

But it seems odd that you observe this only after a water change - how do you perform your water changes?

(eg,
I have a Python system and refill direct from tap (adjusted to water temp 2-4*C cooler than initial tank temp), adding Prime (dosed for entire tank volume) at start of refill and then again at the finish (I used not to do this second dose, but several times noticed some fish distress that immediately cleared with the additional Prime - I’m close to a Chlorine Dosing Station and water board finally admitted that my Chlorine levels can (often) be much higher than the published data)
I typically leave my filter running during water changes - when I kept altums, they immediately ghosted when I stopped the filter, so I adjusted my water change routine)

What is your lighting and CO2 schedule?

(Discus can be quite sensitive to returning water, especially when dissolved gas levels are high - read about micro bubbles or gas bubbles on discus forums)


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## Cat (7 Sep 2020)

Hello everybody,

I 'started a conversation" with Zeus which I thought would visible in the thread because I couldn't find a Reply button but it doesn't appear to be visible so I thought I'd better just respond here instead! (It's been a while.....) Oh I've just seen the quote button oops...

Hogan53 -I didn't realize there was that much dissolved CO2 in the tap water?

and in answer to Alto's question I'll describe my set up. It has a fluidized bed filter inline and a large external sponge filter. It has inline heaters and the Co2 goes through a ceramic diffuser also inline. The tap water comes from mains, using a TRV or "mixer valve", then enters a three cartridge filter; sediment, carbon, chloramine then into the tank.

The lights are homemade 8 x floodlight LED's they come on at 1.00 for 8 hours the CO2 comes on at 10.30 for 8 hours. It start the water change at 7.30 am and it is finished a couple of hours later, it takes a while to drain and to fill. Here is a photo incase it helps sorry its not a very good photo.


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## GHNelson (7 Sep 2020)

http://www.fishyportal.com/cgi-bin/pub/diag?c=v&id=55
Hi 
Try doing two separate 25% water changes when the lights are on!
You can monitor the fish then.


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## Zeus. (7 Sep 2020)

Cat said:


> Oh I've just seen the quote button oops...





Cat said:


> Hi Zeus,
> 
> Thank you for the response. Do you have any idea how long the water would take to degas? It's a long thin tank really so I'm not sure how much the surface area would make to degassing. I also have duck/chick weed in there recently (unintentionally) which I have take out in vast quantities.
> 
> ...





Zeus. said:


> 24hrs and even then it may still contain some. It I take a glass of water out off tank just before co2 on then next day take pH of glass and tank just before CO2 on the glass has a higher pH so lower [CO2]
> 
> Mine lasts months
> 
> ...


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## Cat (7 Sep 2020)

hogan53 said:


> http://www.fishyportal.com/cgi-bin/pub/diag?c=v&id=55
> Hi
> Try doing two separate 25% water changes when the lights are on!
> You can monitor the fish then.




I was doing it first thing to avoid wasting CO2 as I thought that was way that was considered most sensible, but as I seem to have too much CO2 I suppose this isn't a problem!


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## Cat (7 Sep 2020)

Zeus. said:


>




Blimey I had no idea it took so long to gas out!


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## alto (7 Sep 2020)

Do you use water conditioner?
If local water supplier uses chloramine (at any time), I’d suggest Prime (as it binds ammonia)

You mention adding tap water that has gone through a 3stage filter but how is the water quality monitored?

I’ve not used a fluid bed filter (sand?) on an aquarium, what is the flow rate in the tank?
Flow rate through the filter?

Tank looks fantastic, what are the dimensions?

When refilling tank, add water with splashing - this will quickly degas new water, as will filter return with splashing/surface agitation


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## Cat (7 Sep 2020)

Zeus. said:


>



I think I need to prioritise buying new drop checker fluid for sure. Have been experimenting a lot recently with different plant setups after I sold the Discus fish so its been a long time without livestock so got lazy, with CO2 just blasted in there. How do you calculate how long your CO2 should be on for? I find it hard with the large tank as everything takes so long and I've got two young children that need to be constantly ferried about etc. I do have a Ph profile chartso I can attempt that at the weekend. I had turned the CO2 down recently as the stem plants were going so crazy I was cutting a bucket out a week and I was worried removing so much material might change the uptake of CO2 and leave a lot more in the water. Then this chickweed came seemingly from nowhere.... its much finer that the stuff in my pond in my garden I assume it came with some plants I bought at some point. But again it suddenly covers the surface, I presumed that would effect the surface gas exchange also so I've been netting out masses of that too.....


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## Cat (7 Sep 2020)

alto said:


> Do you use water conditioner?
> If local water supplier uses chloramine (at any time), I’d suggest Prime (as it binds ammonia)
> 
> You mention adding tap water that has gone through a 3stage filter but how is the water quality monitored?
> ...



I don't use a water conditioner because we have a specific chloramine cartridge for that, and a carbon filter too. I would go through a bottle a week with a tank this size! The dimensions are 216 cm long x 45cm deep x 54cm high. I do have sand in the fluidized bed, its been a favourite for Discus fish keepers. I cannot remember what the flow rate is, it was originally calculated to produce 10 x the volume an hour (at least) but it probably doesn't do anywhere near that. The spray bar at the back has pretty poor flow ( we drilled the holes too big due to a miscommunication btn husband and I!) so we added the external sponge filter ( which is about 20litres ). I was informed on UKAPS that conventional test kits were so inaccurate they wasn't any point using them so I focus more on water changes and syphoning out crap every week instead.


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## davidgorman74 (7 Sep 2020)

I had the exact same issue a few weeks ago, this explains why now, ended up doing a midnight water change as all the fish looked "drunk"


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## alto (7 Sep 2020)

Cat said:


> I was informed on UKAPS that conventional test kits were so inaccurate they wasn't any point using them


That because you haven’t read my extensive posts on the topic 

The biggest inaccuracy with hobby grade test kits is......
The Hobbyist

(this has been shown many times by aquarium clubs (mostly reef clubs seem to do the experiments), fish magazines etc)

API isn’t my first choice in test kits, but for an economy price they produce a decent kit that will show trends and approximate values for most parameters that are of interest/use to aquarium keepers

Angel fish are NOT one of the ornamental fish species that are particularly sensitive  to “osmotic shock” or moderate pH shifts or moderate CO2 levels
(though you’re perhaps talking about wild caught angels? if so which species?)

That they are showing distress after a water change that should be reducing CO2 (there is extremely low likelihood that your tap water has dissolved CO2 levels anywhere near 30ppm) indicates something changes with this new water
It’s interesting that only the juvenile angels are reacting so visibly


5ml of Prime treats 200litre of water (for actual ammonia and chloramine levels neutralized, check Seachem FAQ etc - the numbers no longer appear on the bottle label) - if you’re only doing 1 x 50% water change per week, a 500ml bottle should last several months

I suggest testing the effect of Prime as this is a very quick check (testing the water quality after the 3 stage filter will likely cost more)

As you mention a spray bar, this should provide loads of “splash” during the water change, so CO2 levels should be significantly lower than when the tank is full and running - or are you turning the filter OFF during water changes?



> I focus more on water changes and syphoning out crap every week instead.


Perfect


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## sparkyweasel (8 Sep 2020)

Cat said:


> I don't use a water conditioner because we have a specific chloramine cartridge for that, and a carbon filter too.


Do you have a protocol for ensuring they are not exhausted?


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## sparkyweasel (8 Sep 2020)

alto said:


> The biggest inaccuracy with hobby grade test kits is......
> The Hobbyist


It's a bit tricky to remove that factor from the equation.


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## alto (8 Sep 2020)

sparkyweasel said:


> It's a bit tricky to remove that factor from the equation.


That’s why test kits that include a reference standard are so useful
(one may still not be able to reproduce a result, but at least one knows it’s happening  ... I’ve used a lot of these  and I was in shock the first time a PostDoc couldn’t use one of these ... only then it turned out not to be an anomaly  )

Unfortunately these were mostly put out by companies such as Salifert, LaMotte, Hach etc so were 1.5 to 2 times the price of the econo kits, and as freshwater hobbyists were unwilling to pay for better quality/traceability ...

Seachem still offers a few kits with reference standards (but even those have dropped steadily from the market, while the test kit may still be available, pricing competition has meant the kits are pared down)


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## JoshP12 (8 Sep 2020)

Hi all,

I experienced something similar a few weeks ago.

I hope I am understanding from what I read:
You water change at 7:30 PM, CO2 off at 5:30 PM and lights still on from 1-9PM - water change completed at 8:30 PM no ramp. Fish show signs of distress at 8:30 PM.

My thought is a sudden”Ish” change in dissolved oxygen levels.

This can very easily be ruled out if right after that water change your plants are pearling intensely.

If you use a holding tank for your water prior to putting in the tank, the the oxygen levels will be lower. I am also not sure how your filtration will Impact O2 levels.

You are water changing at 6.5 hours after lights on - the water at this time is super saturated with oxygen from the plants. If you pull out that water and add lower DIssolved oxygen water, the sudden change may be hard on the livestock.

Just some thoughts! 

Josh


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## Zeus. (8 Sep 2020)

Respiration is mainly driven by the bloods [CO2] esp in mammals, fish do have O2 receptors in their gills however its the high [CO2] in the blood thats dangerous to us and fish as it results in a lower pH of the blood, this change in pH changes the equilibrium of many chemical and biochemical pathways which if not corrected can be fatal.

Apollo 13 was a classic example of plenty of O2 but dangerous CO2 levels

Carbon Monoxide is another kettle of fish altogether, it has a high affinity to hemoglobin, over 300x thas of O2, so once attached it blocks the O2 carrying site of hemoglobin, so as respiration is driven by [CO2] (which is carried in the plasma of the bllod) your CO2 levels remain stable you breath normally, fall asleep and don't wake up


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## dw1305 (8 Sep 2020)

Hi all,





JoshP12 said:


> My thought is a sudden”Ish” change in dissolved oxygen levels.


It has to be that.  My guess is that it is CO2 in the tap water. 





alto said:


> That’s why test kits that include a reference standard are so useful


Same for me, I would be very reluctant to use a method that didn't include a standard curve for calibration.

cheers Darrel


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## lazybones51 (8 Sep 2020)

Cat said:


> I don't use a water conditioner because we have a specific chloramine cartridge for that, and a carbon filter too. I would go through a bottle a week with a tank this size! The dimensions are 216 cm long x 45cm deep x 54cm high. I do have sand in the fluidized bed, its been a favourite for Discus fish keepers. I cannot remember what the flow rate is, it was originally calculated to produce 10 x the volume an hour (at least) but it probably doesn't do anywhere near that. The spray bar at the back has pretty poor flow ( we drilled the holes too big due to a miscommunication btn husband and I!) so we added the external sponge filter ( which is about 20litres ). I was informed on UKAPS that conventional test kits were so inaccurate they wasn't any point using them so I focus more on water changes and syphoning out crap every week instead.


Prime is incredibly concentrated, with 5ml treating 200l of water. For the price it's worth doing even if you are using another form of filtration.


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## Cat (8 Sep 2020)

JoshP12 said:


> Hi all,
> 
> I experienced something similar a few weeks ago.
> 
> ...


No I'm doing the water change at 7.30 am fi


sparkyweasel said:


> Do you have a protocol for ensuring they are not exhausted?


Yes we have dates in the


alto said:


> That because you haven’t read my extensive posts on the topic
> 
> The biggest inaccuracy with hobby grade test kits is......
> The Hobbyist
> ...



Always used them 20 years ago when I wasn't keeping plants, they seemed reasonable enough to show general trends, mind you whatever they said you ended up doing the same thing ie a water change. We used them when we did the fishless cycling with ammonia etc.....
calender to change them but we are changing now again anyway because they were doing work in our road a few days ago which resulted in running brown bath water


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## Cat (8 Sep 2020)

sparkyweasel said:


> Do you have a protocol for ensuring they are not exhausted?


We have dates written in the calender, although we were about to change them early anyway as there was some work going on in the road and it made the water run brown for half a day so we thought that may have saturated the carbon filter. That was a few days ago though and this hypoxia after a water change has happened before with the Discus so I thought it was worth asking the question anyway.


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## Cat (8 Sep 2020)

I'll order some I think, just in case, it'll be better than hurting the fish...


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## dw1305 (8 Sep 2020)

Hi all, 





Cat said:


> although we were about to change them early anyway as there was some work going on in the road and it made the water run brown for half a day


"Prime" is a good idea. <"Your tap water"> will almost certainly have been treated with an <"emergency" chloramine dosing">.

cheers Darrel


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## Cat (8 Sep 2020)

dw1305 said:


> Hi all, "Prime" is a good idea. <"Your tap water"> will almost certainly have been treated with an <"emergency" chloramine dosing">.
> 
> cheers Darrel


 
Cambridge water seems to do this quite a lot!


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## Cat (8 Sep 2020)

JoshP12 said:


> You water change at 7:30 PM, CO2 off at 5:30 PM and lights still on from 1-9PM - water change completed at 8:30 PM no ramp. Fish show signs of distress at 8:30 PM.



I change the water at 7.30 am whole water change is finished before 10.30 when the Co2 comes on for 8 hours and the lights go on at 1.00pm for 8 hours. This was so we'd actually get a chance to see the tank with it's light on as we are usually out most of the day.


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## dw1305 (8 Sep 2020)

Hi all, 





Cat said:


> Cambridge water seems to do this quite a lot!


The limits on faecal coliform in drinking water are <"really strict"> (and they need to be), but one knock effect of this is that any potential breach in the integrity of the water main is likely to be met by emergency chloramine dosing.

Anywhere in the <"SE of England"> is likely to experience the triple whammy of <"shortage of supply, agricultural pollution"> and a <"lot of new builds">.

cheers Darrel


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## Cat (8 Sep 2020)

dw1305 said:


> Hi all, The limits on faecal coliform in drinking water are <"really strict"> (and they need to be), but one knock effect of this is that any potential breach in the integrity of the water main is likely to be met by emergency chloramine dosing.
> 
> Anywhere in the <"SE of England"> is likely to experience the triple whammy of <"shortage of supply, agricultural pollution"> and a <"lot of new builds">.
> 
> cheers Darrel


Describes Cambridge perfectly! We have really high nitrates as well, at the limit last time I checked apparently from fertilizer run off. I don't suppose you would have any idea why we only seem able to get a breakdown of the water readings/test results from 2 years ago and none more recently? I emailed them once about phosphate and they emailed me back 9 months later with a phosphate measurement!


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## jaypeecee (8 Sep 2020)

Hi @dw1305 


dw1305 said:


> My guess is that it is CO2 in the tap water.



Do you happen to know how much CO2 is in tap water? And, is it the result of atmospheric CO2 or is it added by water companies?

JPC


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## dw1305 (8 Sep 2020)

Hi all, 





Cat said:


> I don't suppose you would have any idea why we only seem able to get a breakdown of the water readings/test results from 2 years ago and none more recently? I emailed them once about phosphate and they emailed me back 9 months later with a phosphate measurement!


No, not really, usually you should be able to get water results for the previous year.

The issue with phosphates is that there isn't a legal limit, so they don't have to measure PO4---, basically they can't be in breach of the EU limits, because there isn't one. Elevated levels of phosphate in water are associated with algal blooms etc, so you may get a <"phosphate stripper"> at a sewage works, but there aren't any particular health issues for humans.

Water companies actually add PO4--- to drinking water so that it <"can precipitate out any lead (Pb)"> etc.





jaypeecee said:


> is it the result of atmospheric CO2 or is it added by water companies?


I think normally it is just because the water in the main is cool and under pressure, meaning that it can hold more dissolved gases.

Water companies try and avoid too much CO2 in the water main, because it depresses pH and makes metal solubilisation more likely.

cheers Darrel


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## jaypeecee (8 Sep 2020)

dw1305 said:


> I think normally it is just because the water in the main is cool and under pressure, meaning that it can hold more dissolved gases.


Thanks, Darrel.

That would make sense.

JPC


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## sparkyweasel (8 Sep 2020)

Cat said:


> Cambridge water seems to do this quite a lot!


That could exhaust your filter sooner than expected. It wouldn't hurt to change it early.


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## alto (9 Sep 2020)

Cat said:


> I'll order some I think, just in case, it'll be better than hurting the fish...



Prime keeps for ages, and it can be useful to have on hand
(It’s worth reading though the Seachem FAQ and Discussion Board posts - if it manages to come back online)

Your water prefilter system should be working (though there are enough anecdotal reports of problems that it’s always something I suggest checking)

Typically ground water will have dissolved CO2 levels of less than 10ppm, though deep ground water measurement may be much higher (eg, 100ppm though I don’t know how typical these much higher values may be), but it also doesn’t take much swirling or agitation to reduce this dissolved CO2 level

If this effect is something you’ve noted over the years, I’d be inclined to pick up a Hach CO2 test kit
If you’re interested in doing this, I’d suggest some reading first so you understand the limitations of this methodology
The Krib (always a good resource - though this summary is a bit digressive)
https://www.thekrib.com/Plants/CO2/test-kits.html#1

Aquaculture facility notes on using this Hach test kit
http://agrilife.org/fisheries2/file...-Instructions-for-Hach-Water-Quality-Kits.pdf

Open access article - there may be more suitable studies but this one offered an accuracy comparison with the CO2 titration method - only Test Series 1 is notable as it examines  CO2 measurement in freshwater

*Comparative performance of CO2measuring methods: Marine aquaculture recirculation system application*
https://www.sciencedirect.com/science/article/pii/S0144860910000683



> Test Series I results are summarized in Table 1. Barometric pressure (BP) was stable at 749 mm Hg, the total dissolved solids concentration was approximately 0.6 g/L, water temperature and dissolved oxygen ranged between 15.2–15.6 °C, and 10.1–10.7 mg/L, respectively. The differences between readings from the two HSU readings were small, ranging between 0.1 and 0.2 mg/L. Precision of the HSU readings, as measured by the coefficient of variation (CV = [100 × SD]/mean), ranged from 0.93 to 3.72 and averaged 1.85% for the two units. The precision of the HSU output was better than that determined for the CO2 probe (4.09%), and the titrimetric method (5.84%). HSU based DC results were lower than those measured by the CO2 membrane probe or the titration method.
> 
> As shown in Table 1, at the low CO2concentration there was no difference between the head space units and the CO2 probe.
> The CO2 concentration determined using HSU 1 and 2 were 21.5 ± 0.8 and 21.6 ± 0.2 mg/L and the CO2 probe was 22.7 ± 0.8 mg/L (mean ± SD)
> ...


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## dw1305 (9 Sep 2020)

Hi all, 





alto said:


> but it also doesn’t take much swirling or agitation to reduce this dissolved CO2 level ...............If this effect is something you’ve noted over the years, I’d be inclined to pick up a Hach CO2 test kit


It won't give you a quantitative value, but there is actually a really quick visual test you can use if  you have hard (carbonate rich) tap water, like @Cat. 

Just run the cold tap for a little while (couple of minutes) and then draw a glass of water. Ideally you want plain glass, something like a pint sleeve glass. You also need reasonable light and a dark back-ground. 

If there is appreciable levels of dissolved CO2 you will see calcium carbonate form and precipitate out as the CaCO3 scale. Often all you get is a slight "milkiness" and the  limestone scale isn't obvious as a precipitate in the glass. 

cheers Darrel


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## Cat (9 Sep 2020)

Zeus. said:


> Respiration is mainly driven by the bloods [CO2] esp in mammals, fish do have O2 receptors in their gills however its the high [CO2] in the blood thats dangerous to us and fish as it results in a lower pH of the blood, this change in pH changes the equilibrium of many chemical and biochemical pathways which if not corrected can be fatal.
> 
> Does the pH of the tank water directly effect the blood pH?


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## Cat (9 Sep 2020)

dw1305 said:


> Hi all, It won't give you a quantitative value, but there is actually a really quick visual test you can use if  you have hard (carbonate rich) tap water, like @Cat.
> 
> Just run the cold tap for a little while (couple of minutes) and then draw a glass of water. Ideally you want plain glass, something like a pint sleeve glass. You also need reasonable light and a dark back-ground.
> 
> ...



I have a Hanna pen that does TDS, uS and pH, so I know I have high solids and can do pH easily before and after water changes and test straight from the tap. I presume a CO2 test would only be valid for a relatively short while as it gasses off? My husband is an electronic engineer and is interested in making a pH test that would measure the pH constantly ( out of interest more than anything else ) but its probably going to be a long time before he has any time to do it in reality so we'll probably have to stick with pen for the foreseeable future...


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## dw1305 (9 Sep 2020)

Hi all, 





Cat said:


> I have a Hanna pen that does TDS, uS and pH, so I know I have high solids and can do pH easily before and after water changes and test straight from the tap. I presume a CO2 test would only be valid for a relatively short while as it gasses off?


Yes, you would need to stop the CO2 gassing off, which means minimising the gas exchange surface area. Sealed in a screw top bottle would be fine, it works for carbonated drinks and <"they have an immense amount of dissolved CO2">. 

Conductivity will go up, but that is mainly a temperature, rather than ionic, effect. You can get an <"ion selective electrode"> for CO2, but I've never seen one.

You could look at pH, and you would theoretically get a rise in pH (as the CO2 out-gasses) that could be used to calculate the dissolved CO2 content. This is how  <"drop checker works">. 

The problem is that your tap water contains a lot of dKH (somewhere around 20 dKH), which means that you need a large amount of CO2 dissolved before you get much drop in pH away from the carbonate equilibrium ~pH8 value.   




cheers Darrel


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## Cat (13 Sep 2020)

Hi I just thought I'd let you know I'm doing a water change today. I've added Prime ( I had no idea how concentrated it was amazing stuff!) although it does say that if I'm adding it directly to the aquarium I should dose for the whole tank volume so I have to dose twice as much? I have replaced the carbon and chloramine cartridges too. I'm doing a pH profile today, just out of interest, and I'm doing a profile tomorrow so I've got one without a water change in it.

Thank you for all your advice.


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## lilirose (13 Sep 2020)

Cat said:


> Hi I just thought I'd let you know I'm doing a water change today. I've added Prime ( I had no idea how concentrated it was amazing stuff!) although it does say that if I'm adding it directly to the aquarium I should dose for the whole tank volume so I have to dose twice as much? I have replaced the carbon and chloramine cartridges too. I'm doing a pH profile today, just out of interest, and I'm doing a profile tomorrow so I've got one without a water change in it.



If you're adding it directly to the tank, yes, you have to dose for the whole tank.


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