Yes you can. I often hear that referred to as 'compost tea' or kelp. It isn't cheap but it's great for getting plants off to a good start. Use as a supplemental feeding with good rich compost. The ratio depends on the concentration of your product & the instructions should be on the label. A couple capfuls to a gallon of water is sufficient. Tomatoes are heavy feeders so apply every 2 weeks of only what the plant can use. Add some garden lime when planting to prevent 'blossom end rot'. That's the worst! It lowers the soil ph so the tomato plant is able to take up calcium & magnesium. Those 2 elements are vital to our good health anyway. I only grow 4 or 5 tomato plants but have lots of fresh tomatoes to eat every day with enough left over to feed the neighbor and donate to the soup kitchen.

Thankyou very much, great advice.