If you’ve been trying to unlock the Acidgrinder Rod in Fisch and got confused halfway through the questline, don’t worry because this one is honestly more complicated than most rods in the game. You are going to bounce between mutations, special rods, Brine Storms, and some pretty rare fish before finally getting your hands on it.
I spent some time breaking the whole process down into simple steps so you can actually follow it without constantly rewatching videos or asking people in chat what to do next.
The biggest thing to know before starting is this: most of the quest takes place around Desolate Deep and the Brine Pool, so prepare for a bit of grinding.
Where to Start the Acidgrinder Rod Quest
First, head over to the Underground Music Venue and talk to Axel. He’s the NPC that gives you the full Acidgrinder Rod questline.
Once you speak with him, you’ll get several fishing objectives that need special mutations and specific fish. This is where most players get stuck.
Step 1: Catch a Tainted Brine Phantom
Your first task is catching a Tainted Brine Phantom.
The important part here is the Tainted mutation. You cannot get this mutation with normal rods. You specifically need the Bloomspire Twisted Toxins Rod because it’s currently the only rod capable of giving fish the Tainted mutation.
How to Get the Bloomspire Twisted Toxins Rod
To unlock this rod:
- Go to the Living Garden
- Buy the Bloomspire Rod first
- Use a Toxic Lotus on it to transform it into the Bloomspire Twisted Toxins Rod
Now, to get the Toxic Lotus:
- Plant a Rotten Seed inside the Living Garden
- Wait for it to grow into a Toxic Lotus
Yeah, it sounds like a lot just for one mutation, but Fisch loves making players do side progression before quest progression.
Where to Catch the Brine Phantom
The Brine Phantom is found inside the Brine Pool area at Desolate Deep.
Once you catch one using the Bloomspire Twisted Toxins Rod, there’s a chance it becomes Tainted. Keep fishing until you finally get the mutation.
After that, return it to Axel.
Step 2: Catch a Brined Brine Sovereign
The second quest objective asks for a Brined Brine Sovereign.
This part is honestly the grindiest section because the Brine Sovereign itself is already an Exotic fish.
Rod Needed for the Brined Mutation
You need the Brine Infused Rod for this mutation.
This rod can be purchased at the Brine Pool for 75,000 Coins.
The rod gives a 50% chance to apply the Brined mutation while fishing.
How to Find the Brine Sovereign
The Brine Sovereign only appears:
- Inside Desolate Deep’s Brine Pool
- During a Brine Storm
This means you either:
- Wait for rainy weather and hope the event starts naturally
- Or use a Brine Storm Totem
A lot of players recommend using totems because waiting for random weather can take forever.
There’s also a chance Axel’s earlier quests reward one, so check your inventory before spending extra resources.
Once the storm begins, start fishing for the Brine Sovereign and hope the Brined mutation applies with your Brine Infused Rod.
This step can take a while because you’re dealing with both RNG fish spawns and mutation chances at the same time.
Step 3: Catch an Acidic Caustic Starworm
Now comes the final objective before unlocking the Acidgrinder Rod.
You need an Acidic Caustic Starworm.
How to Get the Acidic Mutation
There are two ways to apply Acidic:
- Acidgrinder Rod itself gives a 40% Acidic mutation chance
- Acidic Lava Bait gives a guaranteed 100% Acidic mutation chance
Since you obviously don’t have the Acidgrinder Rod yet, using Acidic Lava Bait is the easier method here.
Where to Find the Caustic Starworm
The Caustic Starworm is a Secret fish that appears:
- Inside the Brine Pool
- During a Brine Storm
So yes, you are going back to the Brine Pool again.
At this point, you’ll probably know the area better than your own spawn island.
Once you finally catch the Acidic version of the fish, return it to Axel to complete the questline.