I hope you meant 2ml per 10 gallons, Jeff, otherwise I'm way off.
You said to add more as needed, how do you determine if more is needed? Is there harm in overdosing traces? I'm suffering from what I believe to be some sort of deficiency, but I can't pinpoint it. I haven't looked at traces though, so any help here would be appreciated. I'm mixing 2.5teaspoons in 250ml water and dosing 5ml every other day in my 20.
Yes per 10 gallon. What deficiency are you seeing? I would guess more then likely the deficiency you are seeing is CO2 related. Crank it UP! Based on what you are dosing in your 20 I dont think you would be lacking any traces or Fe.
My plants go through "droopy" phases here and there, and they're not uptaking any NO3 or PO4 based on my test kits (which are obviously suspect as their accuracy is questionable). But even if they're "off" I'd think I'd see a change over time. I suspected this was a deficiency that was causing the plants to not suck in the nutrients, but I could be wrong. The CO2 is cranking, I hang around 36ppm. I'm also dealing with GSA and Hair/Thread algae.
IF you are measuring CO2 based on PH and KH that can also be inaccurate. To many factors can give you a false KH reading by buffering your water. Sometime when you will be around to watch the fish, turn the CO2 up a little, watch the fish for signs of distress. If they start hovering near the top turn it down and get some surface movement going.
I do use kH/pH method, since I don't know of a better way. My test right now shows 60ppm, so I'm accounting for some inaccuracies. Fish seem fine, so I'll leave it be I guess.