diff --git a/codex/merkletree/merkletree.nim b/codex/merkletree/merkletree.nim
index 9b972e88..fab6476d 100644
--- a/codex/merkletree/merkletree.nim
+++ b/codex/merkletree/merkletree.nim
@@ -121,7 +121,6 @@ func reconstructRoot*[H, K](proof: MerkleProof[H, K], leaf: H): ?!H =
 func verify*[H, K](proof: MerkleProof[H, K], leaf: H, root: H): ?!bool =
   success bool(root == ? proof.reconstructRoot(leaf))
 
-# TODO: replace with implementation in poseidon library plz
 proc merkleTreeWorker*[H, K](
   self: MerkleTree[H, K],
   xs: seq[H],
diff --git a/codex/slots/proofs/prover.nim b/codex/slots/proofs/prover.nim
index 956270c2..ab1ed687 100644
--- a/codex/slots/proofs/prover.nim
+++ b/codex/slots/proofs/prover.nim
@@ -66,6 +66,10 @@ proc prove*(
     error "Unable to create slots builder", err = err.msg
     return failure(err)
 
+  if err =? (await builder.init()).errorOption:
+    error "Failed to initialize builder", err = err.msg
+    return failure(err)
+
   without sampler =? AnySampler.new(slotIdx, self.store, builder), err:
     error "Unable to create data sampler", err = err.msg
     return failure(err)
diff --git a/codex/utils/poseidon2digest.nim b/codex/utils/poseidon2digest.nim
index efc9acfe..3960ca0c 100644
--- a/codex/utils/poseidon2digest.nim
+++ b/codex/utils/poseidon2digest.nim
@@ -55,7 +55,7 @@ proc digestTree*(
       return failure err
     leaves.add(digest)
     index += chunkSize
-    await sleepAsync(1.micros) # cooperative scheduling
+    await sleepAsync(1.nanos) # cooperative scheduling
   return await Poseidon2Tree.init(leaves)
 
 proc digest*(
diff --git a/tests/codex/slots/backends/testcircomcompat.nim b/tests/codex/slots/backends/testcircomcompat.nim
index 99097afd..d8cb1021 100644
--- a/tests/codex/slots/backends/testcircomcompat.nim
+++ b/tests/codex/slots/backends/testcircomcompat.nim
@@ -99,6 +99,7 @@ suite "Test Circom Compat Backend":
           cellSize)
 
     builder = Poseidon2Builder.new(store, verifiable).tryGet
+    (await builder.init()).tryGet()
     sampler = Poseidon2Sampler.new(slotId, store, builder).tryGet
 
     circom = CircomCompat.init(r1cs, wasm, zkey)
diff --git a/tests/codex/slots/sampler/testsampler.nim b/tests/codex/slots/sampler/testsampler.nim
index 01855c27..d98af204 100644
--- a/tests/codex/slots/sampler/testsampler.nim
+++ b/tests/codex/slots/sampler/testsampler.nim
@@ -111,6 +111,7 @@ suite "Test Sampler":
 
     # create sampler
     builder = Poseidon2Builder.new(store, verifiable).tryGet
+    (await builder.init()).tryGet()
 
   teardown:
     await store.close()