What nutrient mix

[Nuttyneddy]

I have been using a soluble fertilizer with main ingredients 27% Nitrogen,4%Phosphorous ,8.9%Pottasium and 5%Sulphur. Plus micro nutrients. I also put a seaweed solution and some Ebsom salts.
My capacity of water is about 10 litres. I use 4teaspoons of soluble fertiliser mix 1teaspoon of Ebsom plus 20ml of seaweed solution. This mix doesn't seem to be working working very well. My PH is 5.5 . Should I be using a 20 20 20 mix. What mix would you recommend. My system is working on a drain ebb timing running every three hrs for 10minutes.