This is an 8-month old Peace Lily. The plant had started browning about a month ago. I water it once in 3days and fertilize it with sea-weed solution once in 15 days. It sits nearby a window that gets semi-bright but indirect sunlight throughout the afternoon. The plant doesn't seem dead because new leaves and several buds come up but they start browning the same day as well. The leaf size has reduced drastically. The new leaves are much smaller and thinner now; the buds have become tiny too. How do I make my plant lively again? Thanks in advance.
The browning from the tips (tip-burn) leads me to think it is either not watered, or there are too much dissolved salts. Remove excess salts (from seaweed solution) by slowly overwatering once so water leaves the pot.
As said in the comments, your plant looks as if its in too big a pot for its rootball - find a pot that's just slightly larger than the rootball of the plant and repot into that. It should have drainage holes, obviously.
Your plant looks as if its trying to grow, but its being checked by something all the time - move it away from the window if it gets any sunlight at all, they really don't appreciate it, better to give it lower light conditions than exposure to sun. In regard to watering, you may need to adjust your watering routine; water when the surface of the soil feels dry to the touch, but not too dry, and water thoroughly with plenty of water, allowing excess to drain away freely and empty out the tray at the bottom after 30 minutes, and again if it fills up with water once more. Check it a day or so later to see if its already dry again; if not, don't water until it is a little dry on top.
In regard to seaweed fertilizer, whilst that is useful for the soil, it does not directly provide nutrients to plants, so if you can find a proper liquid or water soluble houseplant food such as this https://www.solabiol.com/en/baby-bio-houseplant-food, or something with a similar N-P-K of roughly 10-4-2, then use that instead according to the instructions on the container.