Its a 55g tank & it has 6 or 7 swordtails,2 platys, 1 giant danio, 4 von rio tetras, 1 albino tetra & 2 loaches. My fiance changes 20 to 25% of the water every 2 wks. We can get tetras & giant danios to live for 2 or 3 yrs but can only get the swordtails to live 3 months i dont get it. Do i need to b changing their water more often?