Why is this happening?

I will not be able to get that tub because of the fact i have no space other wise i would have bought a regular tank maybe even a 125 -300 gal tank. I can live with the fact that my fish are dieing. I am willing to put all the filtration that is nessary to keep things the way they are with the same tank.
 
Just to let you know i never replaced the little one tht i had with a bigger one. You are confused. I kept the small one and then when you said get rid of it you have too many fish i got rid of it.
 
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