diff --git a/tests/fluidsim.cpp b/tests/fluidsim.cpp
index 4fb8d14..b9c03c2 100644
--- a/tests/fluidsim.cpp
+++ b/tests/fluidsim.cpp
@@ -29,42 +29,27 @@ int main() {
 
     for (int frameIdx = 0; frameIdx < TOTAL_FRAMES; ++frameIdx) {
         
-        // --- Spawning Logic ---
-        // Spawn throughout the simulation (e.g., until 90% completion)
         if (frameIdx % 10 == 0) {
-            if (frameIdx < (TOTAL_FRAMES * 0.9f)) {
+            if (frameIdx < (TOTAL_FRAMES * 0.1f)) {
                 float t = static_cast<float>(frameIdx) / (TOTAL_FRAMES * 0.9f);
-                
-                // Linear interpolation for Mass: Heavy (10.0) -> Light (0.5)
-                float currentMass = (1.0f - t) * 10.0f + t * 0.5f;
-                
-                // Linear interpolation for Size: Large (12.0) -> Small (2.0)
-                float currentSize = (1.0f - t) * 12.0f + t * 2.0f;
-
-                // Number of particles to spawn this frame (can increase as they get smaller)
                 int spawnCount = 2 + static_cast<int>(t * 4); 
-
-                sim.spawnParticles(baseParticle, spawnCount, currentSize, currentMass);
+                sim.spawnParticles(baseParticle, spawnCount);
             }
         }
 
-        // --- Physics Step ---
         sim.applyPhysics();
 
-        // --- Render & Save ---
         if (frameIdx % 50 == 0) {
             std::cout << "Rendering Frame " << frameIdx << " / " << TOTAL_FRAMES << std::endl;
             
-            // Generate LODs for faster/better rendering
-            sim.grid.generateLODs();
-
-            // Render frame
-            frame renderedFrame = sim.grid.renderFrame(cam, HEIGHT, WIDTH, frame::colormap::RGB, 4, 4, true, false);
+            frame renderedFrame = sim.grid.renderFrame(cam, HEIGHT, WIDTH, frame::colormap::RGB, 5, 4, true, false);
             
-            // Save to BMP
             std::stringstream ss;
             ss << "output/frame_" << std::setw(4) << std::setfill('0') << frameIdx << ".bmp";
             BMPWriter::saveBMP(ss.str(), renderedFrame);
+            
+        }
+        if (frameIdx % 100 == 0) {
             sim.grid.printStats();
         }
     }
diff --git a/util/grid/grid3eigen.hpp b/util/grid/grid3eigen.hpp
index 9ceee59..53a5125 100644
--- a/util/grid/grid3eigen.hpp
+++ b/util/grid/grid3eigen.hpp
@@ -647,7 +647,7 @@ public:
     }
 
     bool inGrid(PointType pos) {
-        return root_.contains(pos);
+        return root_->contains(pos);
     }
 
     bool remove(const PointType& pos, float tolerance = 0.0001f) {
@@ -792,6 +792,15 @@ public:
         }
     }
 
+    bool move(const PointType& pos, const PointType& newPos) {
+        auto pointData = find(pos);
+        if (!pointData) return false;
+        if (!remove(pos)) return false;
+        return set(pointData->data, pointData->position, pointData->visible, pointData->color, pointData->size, 
+                   pointData->active, pointData->objectId, pointData->light, pointData->emittance, 
+                   pointData->refraction, pointData->reflection, pointData->shape);
+    }
+
     bool setObjectId(const PointType& pos, int objectId, float tolerance = 0.0001f) {
         auto pointData = find(pos, tolerance);
         if (!pointData) return false;
diff --git a/util/sim/fluidsim.hpp b/util/sim/fluidsim.hpp
index 504a5d3..841e664 100644
--- a/util/sim/fluidsim.hpp
+++ b/util/sim/fluidsim.hpp
@@ -23,14 +23,13 @@
 #include "../stb/stb_image.h"
 
 struct fluidParticle {
-    Eigen::Matrix<float, 3, 1> pos;
     Eigen::Matrix<float, 3, 1> velocity;
     Eigen::Matrix<float, 3, 1> acceleration;
     Eigen::Matrix<float, 3, 1> forceAccumulator;
-    float density;
-    float pressure;
-    float viscosity;
-    float restitution;
+    float density = 0.0f;
+    float pressure = 0.0f;
+    float viscosity = 25.0f;
+    float restitution = 500.0f;
     float mass;
 };
 
@@ -108,17 +107,21 @@ public:
 
     }
 
-    void spawnParticles(fluidParticle toSpawn, int count) {
+    void spawnParticles(fluidParticle toSpawn, int count, bool resize = true) {
         TIME_FUNCTION;
+        float size = toSpawn.mass / 10;
+        Eigen::Vector3f color = buildGradient(toSpawn.mass / 1000, gradientmap);
+        std::cout << "spawning " << count << " particles with a mass of " << toSpawn.mass << " and a size of " << size << std::endl;
         for (int i = 0; i < count; i++) {
             Eigen::Matrix<float, 3, 1> pos = posGen();
             int id = nextObjectId++;
             
-            Eigen::Vector3f color = buildGradient(toSpawn.mass / 1000, gradientmap);
-            grid.set(toSpawn, pos, true, color, 1, true, id, false);
+            grid.set(toSpawn, pos, true, color, size, true, id, (toSpawn.mass > 100) : true ? false, 1);
             idposMap[id] = pos;
         }
-        newMass -= newMass / 10;
+        if (resize){
+            newMass -= newMass * .01;
+        }
     }
 
     void applyPressureDensity() {
@@ -172,27 +175,39 @@ public:
     }
 
     void replaceLost() {
-        int toReplace = 0;
-        #pragma omp parallel for
+        std::vector<size_t> idsToRemove;
         for (auto& point : idposMap) { 
             if (!grid.inGrid(point.second)) {
-                grid.remove(point.second);
-                toReplace++;
+                idsToRemove.push_back(point.first);
             }
         }
-        fluidParticle newParticles;
-        newParticles.mass = newMass;
-        spawnParticles(newParticles, toReplace);
+
+        for (size_t id : idsToRemove) {
+            grid.remove(idposMap[id]);
+            idposMap.erase(id);
+        }
+
+        if (!idsToRemove.empty()) {
+            fluidParticle newParticles;
+            newParticles.mass = newMass;
+            spawnParticles(newParticles, idsToRemove.size(), false);
+        }
     }
 
     void applyPhysics() {
         TIME_FUNCTION;
-            ///TODO: 
-            // apply velocity to have particle move
-            // use mass of neighboring particles to change direction towards them
-            // ressure pushes particles away if they are too close
-            // resitution controls how much pressure builds up based on how close particles are
-            // have to find a way to have a clump use their combined mass instead of individual mass.
-            //if a particle leaves the grid, destroy it and spawn a new one
+        applyPressureDensity();
+        applyForce();
+
+        for (auto& point : idposMap) {
+            auto node = grid.find(point.second);
+            if (!node) continue;
+            Eigen::Matrix<float, 3, 1> acceleration = node->data.forceAccumulator / node->data.mass;
+            node->data.velocity += acceleration * config.TIMESTEP;
+            Eigen::Matrix<float, 3, 1> newPos = point.second + (node->data.velocity * config.TIMESTEP);
+            idposMap[point.first] = newPos;
+            grid.move(point.second, newPos);
+        }
+        replaceLost();
     }
 };