>> I am feeding my fish a medium sized pinch a day. I have 4 common gold fish. I was just wondering If what I was feeding them was enough. When I fed them twice a day they pooped A LOT.
Once a day is fine in a small system - the simple fact is that you are better foliar feeding your plants than relying on feed conversion anyway in a small system.
Goldfish can be fed every other day with a quality feed and if ever needed to stabilise a system chemistry can go for a week no problem. So you wont be under feeding them.
It depends a lot on the feed itself, a lot of flake type foods for instance are not that great.
Pellets are generally better - though you must be careful to have lower protein (30% or so).
As you have a small tank it wont matter much whether you use pet food pellets or get a quality feed.
If they are producing excess solids then it is too much and/or the quality of the food is not very good.
>> Probably bout 9 gallons right now in the tank and 2 cu. ft. of grow medium
presume 2 cu.ft ~ 15 Gal(US)
30 Litres and 60 litres grow medium. (9L per fish = OK)
The size of the tank is important since it determines how much the fish can forage for algae etc and the capacity of the tank to have excess food etc.
Definitely do not overfeed as in a small system it will quickly build up the ammonia and nitrates.
As Yav notes get yourself an aquarium freshwater test kit to test for pH, Ammonia, Nitrites and Nitrates.
Some aquarium shops will provide this test for you.
The next important questions is how much aeration you have (water cycling and bubblers if applicable) and what you are trying to grow. The amount you feed your fish is also factored in to how much waste the system can process and use.
Don't mix your volume units because very few people still use imperial systems. So it is too hard to compare.
Stay with gallons for example. Of course everyone else around the world would prefer the US to move to metric
A few can use google to convert but...