Thank you for you question and for reaching out to Ask Extension.

Seedlings have a low nutrient requirement and are sensitive to over-fertilizing. First, check whether your potting medium contains any organic (e.g., compost) or inorganic (e.g., nitrate) fertilizers. If your potting medium does contain fertilizer, you may not need to fertilize your seedlings until they are transplanted.

If your medium does not contain any fertilizer or the plants start to appear pale green, you may use a very dilute, water-soluble fertilizer after several true leaves have appeared. House plant fertilizers are generally suitable for seedlings (and often are formulated to have low odor). A balanced, low strength fertilizer like 2-2-2 (N-P-K) is suitable for seedlings. When fertilizer, use a lower rate as indicated on the label or even halve the recommended dose. 

Organic fertilizers, such as those derived from fish/seaweed, will likely produce some odor. Inorganic fertilizers containing mineral nutrients (e.g., ammonium, nitrate) are often odorless. The following are examples of liquid fertilizers that would be suitable (which we do not promote nor endorse):

• Dr. Earth Pump & Grow House Plant Indoor Liquid Plant Food 1-1-1
• Espoma Organic Indoor Houseplant Food 2-2-2 
• Miracle-Gro Seed Starting Plant Food 1-0.5-1

To use the Dr. Earth or Espoma products, simple halve the amount of liquid fertilizer recommended and mix that with the same volume of water. A product like the Miracle-Gro is specifically formulated (i.e., dilute) for seedlings.

If you have additional questions, please don't hesitate to reach out to Ask Extension.