old newbee

[Blue whale]

I am retired since 1986. I liked woodworking and gardening but lately I wanted to try something less strenuous. I previously had 2 twenty gal tanks.Last year I went and bought a 75 gal tank.moderately stocked with various plants.The fish are neons guuramis bearded tetras sword fish bristle nose cats and tiger barbs.I would to learn much more about water parameters and anything else.I recently had a problem with ich.Teated it with meds.some died but about 20 lived.Total fish in tank were 40.Also how much light do I need for this tank .Any advice would be appriciated.Thanks