Cories Moving Very Slowly After One Of Them Died

[Poseidonas]

Hello,
 
I have a 60lt heated aquarium with a filter, a betta, shrimps and snails. There are real plants in the aquarium and snails also.
 
A month ago i bought 2 corys. One cory died after 2 weeks, so i assumed that maybe there was something wrong with that fish.  So i went back to the pet shop last week on Saturday and i bought 2 more cories and 2 more fish that i do not know their names (but i upload a photo of them), because the cory that was alive can not stay alone. I read that they need to be always in groups. But i see that also the two new cories are not acting ok and one (Suzi) moves really slow, when it moves, cause it is mostly on the bottom or on the plants, while the old one (from the first 2 that i bought) is moving all the time and quickly also!
 
On Sunday i changed the water, something like 20% after 3 weeks, that i didn't do it and most of my shrimps died. Suzi, my cory that is not ok, was already not moving quickly since Saturday that i bought her.
 
My water:
NH4 is <0,05 mg/l (ppm) (test JBL NH4)
NO3 mg/l Nitrat mg/l: 50
NO2: ok
Total Harness> 21o d (1 o TH=1,78 o TH=1,253 o e= 17,8 o ppm)
Carbonate Harness: 15 o d (1 o CH=1,78 o TAC= 21,8 ppm)
ph 8
Cl2 mg/l : 0
 
The conditions were from the beginning like this. So nothing changed. But i do not know if they are ok.
 
Before i put the water in the aquarium i leave it in a pot for 24 hours for the chlor to go away and then i add in the water aqua safe. 
 
I feed them with flakes (Tetramin) 5 times a week and Sera Bloodworms twice a week, always in the morning. I put first the food of the Betta and then i soak more food and i put it inside, so that it goes to the surface and the rest of the fish can eat from the bottom.
 
Could it be that the cories are not fed correctly? I read that they need sand and i have gravel. But also in the pet shop they were with gravel.
 
Is it just that in my aquarium cories can not live? Should i just stop trying or am i doing something wrong?
 
Thank you,
Natasa
 
In the photos you can see the whole aquarium and my Betta, the cory on the bottom and the two fish that i do not know the names (but are dark green with white spots and orange fins, move super quickly and they are always together)

 

[StevenF]

 
 
On Sunday i changed the water, something like 20% after 3 weeks, that i didn't do it and most of my shrimps died.

This line is confusing.  Do you go 3 weeks without any water changes?  Are you saying that you didn't do water changes because the shrimp died?

 
My water:
NH4 is <0,05 mg/l (ppm) (test JBL NH4)
NO3 mg/l Nitrat mg/l: 50
NO2: ok
Total Harness> 21o d (1 o TH=1,78 o TH=1,253 o e= 17,8 o ppm)
Carbonate Harness: 15 o d (1 o CH=1,78 o TAC= 21,8 ppm)
ph 8
Cl2 mg/l : 0

your nitrate is high.  It is desirable to keep that below 20ppm.  Your total harness (if I understand the units is 373.8ppm (Very hard water).  And your PH is high.  Please run these tests on your tap water and report those number.
 
I suspect you are not cycling your water frequently enough.  Most people do a 30% to 50% water change once per week.  If you don't do that and only add water to compensate for evaporation you water will get increasingly hard.  YOu water might now be too hard for the fish.  That might explain why one died and why a new one is having problems adapting.  the high nitrate might also cause the one to die and the problems with the new one.  Do water changes more water changes.  Do frequent water changes to get your nitrates and water hardness down.  

 

[Munroco]

Cories often sit at the bottom of the tank, could be your first one is the lively one. Have a look at some videos of cories on youtube and see if its different from how your cories are acting.

 

[eaglesaquarium]

 
Hello,
 
I have a 60lt heated aquarium with a filter, a betta, shrimps and snails. There are real plants in the aquarium and snails also.
 
A month ago i bought 2 corys. One cory died after 2 weeks, so i assumed that maybe there was something wrong with that fish.  So i went back to the pet shop last week on Saturday and i bought 2 more cories and 2 more fish that i do not know their names (but i upload a photo of them), because the cory that was alive can not stay alone. I read that they need to be always in groups. But i see that also the two new cories are not acting ok and one (Suzi) moves really slow, when it moves, cause it is mostly on the bottom or on the plants, while the old one (from the first 2 that i bought) is moving all the time and quickly also!
 
On Sunday i changed the water, something like 20% after 3 weeks, that i didn't do it and most of my shrimps died. Suzi, my cory that is not ok, was already not moving quickly since Saturday that i bought her.
 
My water:
NH4 is <0,05 mg/l (ppm) (test JBL NH4)
NO3 mg/l Nitrat mg/l: 50
NO2: ok
Total Harness> 21o d (1 o TH=1,78 o TH=1,253 o e= 17,8 o ppm)
Carbonate Harness: 15 o d (1 o CH=1,78 o TAC= 21,8 ppm)
ph 8
Cl2 mg/l : 0

 
A few items are smacking me in the face here.  
 
Water changes - You should be changing a minimum of 25% weekly, but closer to 50% weekly is better.  
NH4/NH3 - this should be zero in a cycled tank.
NO2 - I have no idea what 'ok' means.  Either nitrite is ZERO, or its a problem.
pH - 8 - is way too high for most cories.  You never mentioned the specific species of corydoras that you have, but generally, they should have a pH below 7.

 
I suspect you are not cycling your water frequently enough.  Most people do a 30% to 50% water change once per week.  If you don't do that and only add water to compensate for evaporation you water will get increasingly hard.  YOu water might now be too hard for the fish.  That might explain why one died and why a new one is having problems adapting.  the high nitrate might also cause the one to die and the problems with the new one.  Do water changes more water changes.  Do frequent water changes to get your nitrates and water hardness down.  

I think that the water hardness is likely the issue - good catch.
 
 
BTW, Poseidonas, if the tap water is significantly lower than that, you are going to need to SLOWLY correct the issue.  Lots of little water changes will help all the fish.  10% day one... wait a few days... do another 10%... wait a few more days, then 20%.  Wait a few days... 20% again.  I'd suggest adding 10% to each water change every week, with two water changes each week to correct the water.

 

[Poseidonas]

Normally i do every week a 20% change but since i was in holiday (the 2 middle weeks of august), i have not done it for those 2 weeks and when i came back i did the change of the water. I do not just add water. Because i have also gravel that i need to vacuum. I vacuum the complete gravel in 2 times during the month. In the beginning of the month half of the gravel (right side of the aquarium) and after 2 weeks i vacuum the other half. In the weeks between the complete vacuuming i vacuum only the surface. So 2 surface vacuuming per month and 2 vacuumings that are till the bottom of the aquarium.
 
The water in my city is quite hard and i put in the aquarium the tap water after filtering it (i also drink the water after filtering it).
 
I can test the tap water and give the numbers tomorrow but in this 1,5 year that i have the betta i never had a problem with the parameters and with changing the water every week.
 
NO2 "ok" means that is 0. In the test that i have either is ok and it is 0 or it is another color and i have a problem (but this never happened).
 
But can it be such a problem in a 60lt aquarium with filter with a betta, some shrimps, 3 cories and 2 celestial pearl danios? The danios were added last week. The cories a month ago. So till the end of july i only had the betta, shrimps and snails.
 
50% of water change is not too much? I am definitely not an expert but is not going to shock the fish?
 
My cories are pygmy corydoras.

 

[eaglesaquarium]

Normally i do every week a 20% change but since i was in holiday (the 2 middle weeks of august), i have not done it for those 2 weeks and when i came back i did the change of the water. I do not just add water. Because i have also gravel that i need to vacuum. I vacuum the complete gravel in 2 times during the month. In the beginning of the month half of the gravel (right side of the aquarium) and after 2 weeks i vacuum the other half. In the weeks between the complete vacuuming i vacuum only the surface. So 2 surface vacuuming per month and 2 vacuumings that are till the bottom of the aquarium.
 
The water in my city is quite hard and i put in the aquarium the tap water after filtering it (i also drink the water after filtering it).
 
I can test the tap water and give the numbers tomorrow but in this 1,5 year that i have the betta i never had a problem with the parameters and with changing the water every week.
 
NO2 "ok" means that is 0. In the test that i have either is ok and it is 0 or it is another color and i have a problem (but this never happened).
 
But can it be such a problem in a 60lt aquarium with filter with a betta, some shrimps, 3 cories and 2 celestial pearl danios? The danios were added last week. The cories a month ago. So till the end of july i only had the betta, shrimps and snails.
 
50% of water change is not too much? I am definitely not an expert but is not going to shock the fish?
 
My cories are pygmy corydoras.

 
Not at all.  Its the best thing for the fish.  Some diseases can actually be treated with just lots and lots of clean water for the fish to use their own immune system.  Further, even more diseases can be avoided that way as well.  Water changes are just about the best thing to do for your fish.

 

[Poseidonas]

then 50% once a week?

 

[eaglesaquarium]

50% once a week is great for your fish, IMHO.    There are very few occasions where large water changes are bad for your fish.