Hypoxic fish but only after the waterchange?

Cat

Member
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!
 

Zeus.

Member
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?
 

hogan53

Global Moderator
Staff member
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
 

alto

Member
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)
 

Cat

Member
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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Zeus.

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

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.

I find my drop checker very unreliable as it seems to need changing every 4 days or so ( the instruction say 2 weekly ) plus it keeps falling off the glass. Generally it goes from a bluish green to a yellowy green but this process takes a long time so it is yellowy around 9 o'clock.

I change the water at around 7.30 it takes over an hour maybe longer for the water to drain out and come back in, then lights come on at 1.00, the CO2 comes on at 10,30. The fish don't exhibit any problems until about 8.30ish though.

cheers,
Cat

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


which IMO suggests its not fully degassing at night

Thats 8hrs after lights on, does the CO2 need to be on 8hrs after lights on - IMO no plants have had their fill of CO2, which would explain why (pH profile would help confirm this)

little to no uptake off CO2 of plants so [CO2] increases pH increases and fish gasping to drive off the excess CO2 in their blood as their blood becomes to acidic.

Have you done a pH profile ?- well worth the effort IMO but takes some mastering to get the CO2 injection right. From what you have said it sounds like you might not have enough surface agitation

:thumbup:;)
 

alto

Member
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
 

Cat

Member

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.....
 

Cat

Member
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

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.
 
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" :oops:
 

alto

Member
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 :lol:

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
 

alto

Member
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 :lol: 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 :dead: )

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)
 

JoshP12

Member
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
 

Zeus.

Member
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 :arghh:
 

dw1305

Expert
Hi all,
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.
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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