Your aquatic species could develop any level of technology we Telurians (People of Earth) have developed using the same processes we've developed but they might have different motivations.
How they interact with their world will determine the form of their technologies. Do they have two arms or twenty? Do they have fingers or suckers?
Assuming they have a way to manipulate the things in their undersea world, they have to have culture, which gives rise to language, which gives rise to what we consider thought. Thought gives rise to questions, which engender answers and disagreements. All this, obviously, leads to war.
War means better weapons and defenses than the other clams or guys. This means they learn how to construct defensible enclosures out of seaweed, hermit crabs and coral reefs. Which means they figured out how to make tools out of things that can cut seaweed, hermit crabs and so on.
Once they've learned to fight and survive and have time to start questioning why coral is like coral, they can begin to explore the concepts we know as chemistry, physics, and mathematics. Once intelligence and sapient creatures start on that path, there is no turning back since more and more of the world starts making sense, at least until some nabob invents economics and messes everything up for a while. But, that is a different discussion.
Once minds start trying to figure out the world around them using science, they then can figure out to make things they need or want to make their lives longer, safer, healthier, etc. Given their world, they may find ways to create biological solutions were we Telurians depend on physics-based solutions. But, once they have a need, they can find a solution whether how to make electricity or how to melt and purify silicon.
The long and the short of it, pretty soon you have Facebook and StackExchange and sneakers.
Albeit, it's very different from what we would know since they have a very different world than we do, and have different motivations as a result of their environment.