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Fish dying when do a water change

Cory's have the ability to breath air just above the water surface!
This behavior is perfectly normal and is not an indication that anything is wrong with the fish. However, if this is done in excess, it can indicate poor water conditions.
This leads me to believe you had low Oxygen levels prior to dosing Prime...and subsequently after dosing Prime the levels became so low the other fish suffocated.
 
G H Nelson said:
Cory's have the ability to breath air just above the water surface!
This behavior is perfectly normal and is not an indication that anything is wrong with the fish. However, if this is done in excess, it can indicate poor water conditions.
This leads me to believe you had low Oxygen levels prior to dosing Prime...and subsequently after dosing Prime the levels became so low the other fish suffocated.
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I agree this is very plausible.

I really would like to see some (temporary at least) oxygen generation in that aquarium.
 
Hi @Myrkk

Just a couple of quick clips of my tank surface to give you an idea of my surface agitation which helps with oxygenation. It's generated by the filter outflow (spraybar quite weak) and a couple of airstones one at each end of the aquarium). Not saying it's perfect by any means, but maybe useful for illustrative purposes. In all things aquatic I defer to those more experienced than I.



 
Around the surface agitation piece, what you actually want is water that has been exposed to the air at the surface to be transported to the depths of the tank (and vice versa). That doesn't necessarily connect to surface agitation as such because it possible to have a very choppy water surface and yet not get any meaningful exchange into the deep parts of the tank.
 
As I understand it, although no hydrodynamicist, the airstones do generate bottom-to-top circulation by way of the column of bubbles rising to the surface. Whether that also leads to top-to-bottom though, I have no idea!

Another thing that occurred to me was that the duckweed all across the surface probably impedes air exchange to some extent too.
 
White specs are not snails, they are the surface weed being pushed into the tank by the agitation from the filter spray bar. I’ll try and do a video as per LFNFan. I would say my surface agitation is quite good as the water falls like a waterfall into the tank.
I see what you are saying Andy and will be getting an air pump in the mail soon.
I pull duckweed out all the time, last time was 2wks ago, it is growing like billy-o at the moment. I’ve tried getting rid but no luck.
I had 3 corys when we moved here, I now have but one.

I concur that oxygenation is an issue giving the panting of the fish, but given the only thing that has changed is the water supply…
I’ll try RO / rainwater for the next change, do a small one, add an airstone and I’m wondering if adding more carbon filter into the canister will be an idea.

I’m humming and hahing about getting a small tank and switching the fish out then doing a full clean and recycle of the main tank currently, jic old tank syndrome
 
Myrkk said:
I’m humming and hahing about getting a small tank and switching the fish out then doing a full clean and recycle of the main tank currently, jic old tank syndrome
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Earlier you said you replanted last August, so how is your tank old? What do you mean by replanting?
The more I read the less I think this is an old tank syndrom issue to be honest. If you can, do a hardness test of your tank water, in parallel do a hardness test of the tap water. Compare. They should not be that far off. If they are it could be that your dKh is spiking when doing water changes and PH could be fluctuating violently, which fish will not like at all.
Doing water changes with RO or rain water is a good idea but just make sure you remineralize your water. Also start with small volumes of water as your dKh will drop when using soft water.
Also not sure when you last cleaned your filter but it is not a bad idea to do that every couple of months. By cleaning I mean simple rinsing out the excess gunk with water from your tank. This will remove any excess organics that may have accumulated in the filter and could be depriving the tank from oxygen.
 
Because most of us agree this is a water quality issue, I would contact the water company supplier to rule any incidents in the area to rule that out . Esp..with the odd taste from the tap?Perhaps add new stems fast growing oxygenating plants from the sponsers ,change the prime to more easy to administer one like Tetra aquasafe or,Aquarian, agree with regular check on the filter. I don't think we established? the PH ,sudden changes . Which will8affect fish. It's tedious ,it's boring but daily removal of duckweed works replace with frogbit. Salvinia. Small water changes maybe the way to go
 
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Hi all,
Myrkk said:
I concur that oxygenation is an issue giving the panting of the fish, but given the only thing that has changed is the water supply…
I’ll try RO / rainwater for the next change, do a small one, add an airstone
Click to expand...
I think that is a good idea. If you want to add some dGH and dKH? I see <"Oyster Shell Chick Grit"> as the way forward, it is cheap and forms a self-regulatory <"negative feedback loop">. I've always been a <"rainwater user"> and, where it is a viable option, I wouldn't use anything else, .
Myrkk said:
I’ll try and do a video as per LFNFan. I would say my surface agitation is quite good as the water falls like a waterfall into the tank.
Click to expand...
It has to be the tap water, your tank looks fine and you shouldn't be suffering from low oxygen levels, but the fishes behaviour suggests that is the problem. It has to be something in the water adding to the <"Biochemical Oxygen Demand">. That is likely to be <"fixed nitrogen">, because of the rapid duckweed (Lemna minor) growth. The duckweed is working for you (at the moment) as a nutrient sponge.
Myrkk said:
doing a full clean and recycle of the main tank currently, jic old tank syndrome
Click to expand...
That is, honestly, unlikely to help. The problem with a deep clean is that if you reset the tank you will have quite a long time period before you get back to some form of stability. Have a look at <"Seasoned Tank Time">.
Hanuman said:
The more I read the less I think this is an old tank syndrom issue to be honest. If you can, do a hardness test of your tank water, in parallel do a hardness test of the tap water.
Click to expand...
I agree with @Hanuman, normally you can cure <"old tank syndrome"> just by changing some more water. In this case we have worries about the water, so an alternative water source would be useful.

cheers Darrel
 
Myrkk said:
I would say my surface agitation is quite good as the water falls like a waterfall into the tank.
Click to expand...
Waterfall outflows can be deceiving and a poor way to keep water oxygenated. It is a common issue with HOB filters, if the water level of the tank drops because of evaporation, the outflow turns into a waterfall and the oxygenation and water circulation become compromised. A good outflow, in terms of oxygenating the water, would be one that promotes ripples throughout a large area of the water surface, generating a large area of intense gas exchange, and then would move the surface water to the bottom of the tank. Add to that the large area occupied by duckweed, where water ripples and gas exchange area value both get decreased, and you could have a deficiency in gas exchange. This could be amplifying whatever issues you may have with prime or excess of bacterial activity consuming dissolved oxygen.

If the duckweed is not there because you like it, then I would try to keep it in check, with radical removal for a few weeks.
 
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