Errr...Let's try to think "outside of the box".
If you're not having great success using EI+gravel then there is an extremely high probability that either your implementation of EI is inadequate or that there are other factors at play, such as poor CO2 - which is a major factor.
EI by definition provides for more nutrients than the plant can uptake, so why would a substrate change save you?
In any case, if you insist on succumbing to substrate hypnosis then ADA Aquasoil Amazonia is generally accepted as being among the most complete substrate. It's expensive though. Oliver Knotts Nature Soil also seems to be catching on.
Cheers,
