if water perameters have high nitrite/ammonia large water changes (50-75%) every other day helps take it down. i had to do that because my tank had dangerous nitrite levels since it wasnt cycled yet. since u only have a solo flowerhorn it depends on how much u feed him/her. if u feed them alot, they will dirty up your water faster ( poop, food, etc). so, the % water change depends on how good your filtration is. if your tank way over filtrated, then maybe a 25% change every week or so. However, if your tank is under filtrated, a good 30-35% or alittle higher would do. dont do more than 50% though it may stress the fish out.
