There are major problems here. First issue...do not under any circumstance rely on advice from the employees at this store. It has been way off on several issues, which I will address as they are serious. I amnot going to suggest morivation, just stating the fact that according to what you say they advised, they do not have very much knowledge of the requirements of the fish involved.
Second, bettas are not community fish. A male betta is best alone, in a suitably aquascaped tank. Having said that, substrate fish like cories can sometimes work, but sometimes not. If the cories remain on the substrate, the betta may not feel threatened by fish invading his space. But cories need to surface to "breathe," and this means they are continually invading the betta's perceived territory--and a male betta will view the entire tank space when it is this small as "his," period. It would be best to return or rehome the poor cories, not just for this reason but what follows.
Third, the cories. They need sand. Not gravel. They are filter feeders that dig into the sand, take a mouthful and filter out food bits, and expel the sand through their gills. This is how they feed, it is programmed into their genetics so they "expect" it. They cannot do this with gravel. Another issue with gravel-size is bacterial. Rough substrate (the gravel is rough in the photos) is one thing, but gravel harbours uneaten food and this means serious bacterial issues. So the cories are not going to do well in this environment, regardless of the betta.
Fourth...when cories respirate rapidly, there is a serious issue. It takes a bit of time for any new aquarist to recognize normal respiration and abnormal (rapid) respiration, but with cories any sign of rapid respiration must immediately be looked into. This is normal when feeding, because they are charging around. And it wold be normal if two or three decide to engage in spawning activity. But it is not normal at other times, and when spotted, a major water change is advisable. Provided the parameters--these are GH, pH and temperature--between tank water and tap water are basically identical, you cannot do any harm with large water changes. Sometimes this alone solves the respiration, it all depends what is causing it. But we cannot jump to conclusions of "x" or "y" as it often takes much more experience than many of us including me have.
Space. A 10g tqnk really is not large enough for a decent-sized group of cories, and decent size means 9+. More bad advice. These fish are shoaling, meaning they live in huge groups and this too is part of their genetic makeup and they need around 10 or (preferably) more. They are social, but the main reason is simply safety in numbers. They "know" they are more safe the more there are, so stress is increased with fewer. Another reason I would either get a much larger tank, or return/rehome the cories.
I will say nothing about possible dropsy or other disease, I know too little on these issues. I rarely had them over 30 years, one reason being I researched the species and made sure I could provide what it needs, and this goes a long way to healthy fish. We all began not knowing anything, and we had to learn along the way. Even with 30 years, I still learn.
And, welcome to TFF.
Second, bettas are not community fish. A male betta is best alone, in a suitably aquascaped tank. Having said that, substrate fish like cories can sometimes work, but sometimes not. If the cories remain on the substrate, the betta may not feel threatened by fish invading his space. But cories need to surface to "breathe," and this means they are continually invading the betta's perceived territory--and a male betta will view the entire tank space when it is this small as "his," period. It would be best to return or rehome the poor cories, not just for this reason but what follows.
Third, the cories. They need sand. Not gravel. They are filter feeders that dig into the sand, take a mouthful and filter out food bits, and expel the sand through their gills. This is how they feed, it is programmed into their genetics so they "expect" it. They cannot do this with gravel. Another issue with gravel-size is bacterial. Rough substrate (the gravel is rough in the photos) is one thing, but gravel harbours uneaten food and this means serious bacterial issues. So the cories are not going to do well in this environment, regardless of the betta.
Fourth...when cories respirate rapidly, there is a serious issue. It takes a bit of time for any new aquarist to recognize normal respiration and abnormal (rapid) respiration, but with cories any sign of rapid respiration must immediately be looked into. This is normal when feeding, because they are charging around. And it wold be normal if two or three decide to engage in spawning activity. But it is not normal at other times, and when spotted, a major water change is advisable. Provided the parameters--these are GH, pH and temperature--between tank water and tap water are basically identical, you cannot do any harm with large water changes. Sometimes this alone solves the respiration, it all depends what is causing it. But we cannot jump to conclusions of "x" or "y" as it often takes much more experience than many of us including me have.
Space. A 10g tqnk really is not large enough for a decent-sized group of cories, and decent size means 9+. More bad advice. These fish are shoaling, meaning they live in huge groups and this too is part of their genetic makeup and they need around 10 or (preferably) more. They are social, but the main reason is simply safety in numbers. They "know" they are more safe the more there are, so stress is increased with fewer. Another reason I would either get a much larger tank, or return/rehome the cories.
I will say nothing about possible dropsy or other disease, I know too little on these issues. I rarely had them over 30 years, one reason being I researched the species and made sure I could provide what it needs, and this goes a long way to healthy fish. We all began not knowing anything, and we had to learn along the way. Even with 30 years, I still learn.
And, welcome to TFF.
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