5' x 2' x 2' is 150 (American) gallons. EI method is based on American gallons.
1/2 Plantex CSMB
1/2 EDTA Fe
are these also teaspoons? (ie: 1/4 tsp KH2PO4 and 1/2 tsp each CSM+B and Fe?)
EI for this tank would be double this formula (Copied from the sticky at the top of this forum)
50% H20 change-weekly
3/4 Tsp-KN03 3x a week
3/16 Tsp-KH2P04 3x a week
1 Tsp-GH booster once a week
15ml 3/16Tsp-Trace 3x a week
4-8ml-Fe/Iron 3x a week
So I think you are not too far off.
I use the same amount of CSM+B as I use of KH2PO4, and about 25% of that much of iron (I also am using a chelated iron, but I think it is not EDTA Fe)
Do you have a test for NO3?
Note the EI method assumes you are using KNO3, and this is the source of both K and N.
If you are using K2SO4 for some of the K, then the tank might be short of N. You could try using a bit less K2SO4 and a bit more KNO3.
I do the same thing: working back and forth with the K2SO4 and the KNO3, trying to keep the NO3 sufficient but not too high while still supplying the K in sufficient quantity.