There are many different types and brands of fertilizers. What works for some may not work for others. And the variety of seed will also be different for different people.

Even for full grown plants, most horticulturalists are in agreement that commercial fertilizers should be used at half the recommended rate stated on the product.

Commercial fertilizers are salt fertilizers which can burn plants when too much is used. Be cautious, it is always best to dilute commercial fertilizers, especially with seedlings. If you start with a good quality growing medium that is designed for seed starting to begin with, you shouldn't need to use any additional fertilizer at all.

Fertilizers contain salts that can kill the plants you're trying to keep alive, especially if it's allowed to build up. This is because the salt absorbs water more readily than plant roots, effectively starving the grass. Salt itself can also be toxic to plant roots by causing the buildup of sodium, bicarbonate, and boron. Salt injury can cause plants to be more easily susceptible to soil-based plant diseases.

Nature has been growing plants year after year - for millions of years and seasons on it's own - without the help of humans to come along and fertilize with commercial products. Have a little faith in all the hard work nature has put into creating the seed in the first place. Keep it simple and don't try too hard. If you feel you still need to use some, stick with natural fertilizers such as seaweed/kelp, fish emulsion, etc.

In the end, compost (comprised from at least five different sources) is the absolute best fertilizer you can use. You can't use too much of it, it's already at the proper pH, and it's free if you make it!