heres my 430 litre malawi tank
stocked with
6 yellows
2 red empress
red spot pleco
dragonsblood male
ob peacock male
acouple unknow male peacocks
male azureus
male electra
female dolphin
male red top ice blue
two convicts
all these are still young so are growing together
yes you can change the substrate over without replacing tank water.and also the knife will like lower ph than yellows.you will find silica gets dirty quickly aswell
i have just isolated two fish with cloudy eyes.these 2 have been fighting abit so am wondering if its because of this.waterconditions are perfect crystal clear water etc.have just given them salt any other options its just milky like no stringy bits coming off etc