This is a LOW TECH tank, so any answers involving "add CO2" aren't right. Doing the EI isn't right either.
How can you be sure? The pictures look bright. It may be too much light to go without CO2 or heavier dosing.
Pictures can sometimes lie to the eye, so maybe the light isn't as high as it looks. For all I know the light is too low.
Ecocomplete doesn't really have any useable nutrients BTW.
Honestly, it looks like deficiencies across the board to me (Macro, micro, CO2.). I see washed out colors, yellowing, pinholes, browning leaf edges, and stunted new growth.
When there's more than one variable, it can be difficult to pinpoint a specific problem, so why not tell us what size tank you have, and how it's lit. That's a good place to start, and can help us start to narrow down the answer to the problem.