Pond raised fish will always have better colour than indoor tank raised fish. Natural sun will allow algae to flourish. I solved this predicament by having a central filtration system on my fishroom and putting one large tank outside. This outside tank is turned off the system and seeded with a little liquid fertiliser and will go bright green within a week. When its ready, I turn on the inlet tap back on and it will slowly feed the rest of the system. Both adults and fry benefit with a little natural green water occasionally.