Mac Slowing Down When Slack Is Open? Try These Fixes

Slack is supposed to be a chat app. Instead it’s often the largest single RAM consumer on a Mac, capable of using more memory than Photoshop in some configurations. If your Mac feels heavy whenever Slack is in the background, there’s a rational explanation — and several fixes.

Why Slack is so heavy

Slack is an Electron app, like Teams and Discord. Each Slack workspace runs as a separate browser window inside the Electron container. So if you’re in 5 workspaces, you have 5 browser sessions open at all times, each with its own JavaScript runtime, sync engine, and DOM tree.

On top of that, Slack:

• Maintains persistent WebSocket connections to every workspace
• Caches every message you’ve ever loaded for offline viewing
• Renders rich embeds (link previews, images, YouTube cards) on receipt, not on view
• Runs Huddles’ audio infrastructure even when you’re not in a call
• Has gotten increasingly heavy with the AI summary features

A single workspace with light use is fine. Five workspaces with heavy use, plus a Mac with 16 GB RAM and a Chrome habit, is where things break down.

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Check the actual RAM cost

Activity Monitor → Memory tab. Search “Slack.” You’ll see:

• Slack — main process
• Slack Helper (Renderer) — multiple, one per workspace
• Slack Helper (GPU) — graphics
• Slack Helper (Plugin) — for embeds

Add them up. If the total is over 1.5 GB and you’re in just a couple of workspaces, the cache is bloated. If it’s over 3 GB regardless of workspaces, something’s actively wrong.

Fix 1: Sign out of workspaces you don’t actively use

Each workspace is a separate full Slack session. The “I’m in 8 workspaces but only really use 2” pattern is the single biggest cause of Slack RAM bloat.

• Click your workspace icon in the sidebar
• For workspaces you haven’t used in 30+ days: right-click → Sign out

You can sign back in later through your email. The convenience cost is tiny; the RAM win is enormous.

Fix 2: Clear the Slack cache

Slack’s cache grows aggressively. After a year of use, it can be 5+ GB, mostly link preview thumbnails and inline images.

To clear:

1. Quit Slack completely (Cmd+Q, then check Activity Monitor for any leftover Slack processes)
2. Open Finder, Cmd+Shift+G, paste: ~/Library/Application Support/Slack/
3. Look at the size — if it’s over a couple GB, time to act
4. Either delete the entire folder (you’ll re-sign-in to all workspaces) or just the Cache subfolder (less invasive)

The full reset is more thorough. The Cache-only delete is faster but doesn’t catch everything.

Fix 3: Disable hardware acceleration if it’s misbehaving

Like Teams, Slack uses GPU acceleration by default. Like Teams, this is sometimes worse than just running on CPU, especially on Intel Macs.

Slack → Settings → Advanced → Hardware acceleration. Toggle off. Quit and relaunch.

Test it for a day. If your Mac feels lighter, leave it off. If Slack scrolls poorly, turn it back on.

Fix 4: Limit channels you’ve joined

Slack maintains state for every channel you’re a member of. If your work has 200 channels and you’ve joined 80 of them, that’s 80 sets of message history Slack is keeping fresh.

• Channel → settings (gear icon) → Leave channel for ones you don’t actively read

Especially leave the big company-wide announcement channels. You’ll still get @-mentions through DMs.

Fix 5: Turn off unused features

Slack → Settings:

• Notifications → reduce to “All new messages” only for high-priority workspaces
• Audio & video → disable “Show preview before joining a Huddle” if you don’t huddle often
• Accessibility → if you don’t use animations, disabling them saves a small amount of CPU
• Advanced → “Send crash reports” — this isn’t a big drain but it’s an option

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Fix 6: Use Slack in a browser tab

For light use, Slack in a browser is dramatically lighter than the desktop app. You lose:

• Native notifications (browsers can do this, but worse)
• Some keyboard shortcuts
• The ability to launch Huddles without a click

You gain: 1-2 GB of RAM, easier window management, ability to hibernate the tab.

If you’re a heavy Slack user this isn’t viable. If you’re an occasional one, switch.

Fix 7: Restart Slack regularly

Slack has known memory leaks. After a few days running continuously, RAM usage drifts up and never comes back down. The fix is just quitting and relaunching.

I quit Slack every night before bed. Cold-start in the morning is fast, and Monday-morning-Slack is much snappier than Friday-night-Slack.

Fix 8: Check for runaway notifications

If Slack is constantly showing you notification badges and pulling new content from a noisy channel, the constant activity adds CPU drain. The fix is muting the noisy channels:

• Right-click channel → “Mute channel”
• Or in channel settings, change notification preferences to “Mentions only”

Fix 9: Disable preview generation for shared files

When someone drops a file in Slack, the desktop app downloads and renders a preview. For image-heavy channels, this is constant work.

You can’t fully disable previews, but you can skip auto-loading images:

• Slack → Settings → Messages & media
• Uncheck “Show images and files inline”

Links and files still appear, but you click to view them. If you’re in image-heavy design channels, this is a meaningful change.

Fix 10: Watch for the “downloads” cache

Every file someone shares in Slack — and you click on — gets downloaded somewhere. The full cache lives at:

~/Library/Application Support/Slack/Cache/

Files you opened months ago are still there. Slack does some cleanup, but not aggressively. Manual cleanup is fine.

For a thorough cleanup that catches Slack and every other app’s accumulated cache (Discord, Teams, Spotify, browsers, etc.), a smart scanner is faster than going folder by folder.

The wider cleanup angle

Slack’s heaviness compounds with everything else on your Mac. A Mac with:

• 90% full SSD
• 50,000 unread emails sitting in Mail
• A bloated ~/Library/Caches/
• A Photos library being analyzed in the background
• 20 login items auto-launching at startup

…will feel terrible with Slack open, even if Slack itself is fine. Cleaning up the rest of the system makes Slack feel lighter even though you didn’t change anything in Slack.

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A daily Slack hygiene routine

Five minutes that prevents Slack-induced slowdown:

1. Quit Slack at end of day
2. Once a week, sign out of any workspace you didn’t visit
3. Once a month, check Slack’s cache folder size — if over 3 GB, clear it
4. Mute noisy channels (don’t be a hero, mute them)
5. If you don’t huddle, you don’t need Slack open in the background

That’s enough to keep Slack from being the worst app on your Mac. It’ll never be the lightest — that’s just Electron — but it doesn’t have to be the worst either.

What if Slack feels fine but Mac still slow with Slack open?

Then Slack isn’t actually your problem. Check:

• Memory pressure (Activity Monitor → Memory bottom graph) — yellow/red means you’re memory-bound, not Slack-bound specifically
• CPU tab — sort by % CPU, see what’s actually using cycles
• Disk tab — if a non-Slack process is reading/writing a lot, that’s your slowdown

Often the real culprit is something else entirely (Spotlight indexing, photoanalysisd, a Time Machine backup) and Slack just gets blamed because it’s always open.

The honest take

Slack is heavy by design. Microsoft’s Teams is heavier. Discord is heavier still in some configurations. They’re all Electron apps fighting for the same RAM. The fix isn’t switching chat apps — it’s keeping your Mac in good enough shape that the chat app doesn’t matter as much. Free RAM, clean caches, no leftover processes from apps you uninstalled. Slack is then just an annoyance, not a Mac-killer.