When I dropped my lighting from 96 watts to 72 watts nothing at all changed for about a month, then the plants gradually began growing slower. The plants that are right squarely beneath the bulbs still grow as if the lighting were more intense, but other plants don't. Why aren't you just dosing per the EI recommendations? The overdose, if it is one, will do no harm as long as you continue to do weekly 50% water changes, and then you can be sure the plants will not be short of ferts.

But, again, since you are not using CO2, just Excel, your plants may not be short anyway. Excel isn't equivalent to CO2 in it's effect on plant growth. One more point - Excel for a 45 gallon tank gets pretty expensive fast, especially with routine weekly water changes. So, you aren't saving a lot of money by not going to pressurized CO2. I can't remember anyone ever saying they regretted going to pressurized CO2.