K. thx for ur help chester.If you're not using it yet I think I would start ... I'd try 1/2 tsp worked into the top of the soil about once a week per pot ... if you're already using it keep doing what ever you're doing and let us know what it is ...
Let me amend that advice ... I think I would apply 1/2 tsp per pot and water it in ... at the first sign of yellowing I'd do it again ... that is purely a guess ...