EI or dry ferts. Make your own. TPN+ may be a nice fertilizer, but seriously why so expensive? My EI ferts costed me $30 about 18 months ago I'm still not though them. IMO you should be able to sell plants for more than you grow them. So what if I got to weigh powders and mix them into solution about every month. A 500ml bottle of TPN cost $20 and will only last me 5.5 months at best. IMO dry ferts are the only reasonable method for fert large tanks. It may take a little while to figure out the dosing and method, but it that is to be expected in this hobby.