Liquid seaweed is normally an additive (e.g. micro nutrients) as opposed to a fertilizer (macro nutrients). It is often used as a supplement to a regular fertilizer program.. not instead of..

A liquid seaweed fertilizer often contain iron, manganese, etc e.g/ a lot of the micronutrients which the main fertilizers may lack.

I don't know which product you bought and if any nitrogen, phosphorus and potassium is included ?
Does it have a NPK rating ??

Impatiens are very light feeders e.g. they should not be given much nitrogen, and feeding with a high nitrogen fertilizer will result in tall, lush plants but with few flowers.

Fish fertilizers (Fish Emulsion) usually comes in ratios such as 5-1-1 NPK e.g. a lot of nitrogen compared to phosphorus/potassium.

If what you have is the seaweed additive (e.g. supplies micro nutrients, but not N-P-K) then it is ok to use in addition to your usual fertilizer (not instead of). If the product you bought has high nitrogen compared to phosphorus/potassium (e.g. such as 5-1-1) then don't use it. YOu will end up with no flowers.

I use Mor-Bloom from Alaska (fish based) to fertilize impatiens. It provides no nitrogen but plenty of phosphorus and potassium. I alternate it with a regular 20-20-20 synthetic fertilizer which I apply very very sparingly and extremely diluted. In this way you get many more blooms.

Here is a link that might be useful: mor-bloom