Q: Wifi is incredibly slow on OS X El Capitan

Good. When I spoke to Apple tech support, we looked at my apps. I presume he was looking for particular apps that may have been slowing things down, as you describe. We did find a malware app but deleting it did not solve the problem for me, but it was interesting that that's the direction he went towards a solution.

But as I mentioned, my solution was to create a new account. I backed up my account and then used Migration Assistant to bring everything into the new account.

Great ideas dominic23- thank you.

If I add:

~ Also, unplug the coax cable from the router while it sits for a minute then reattach then plug it back in. . .

Would that make sense to you?

I've been advised by Comcast to do so but not sure why.  Had never heard of it previously.

Thank you

Patrick

Can Apple just please fix the bug? I mean how hard can it be to run some tests for all systems that support El Capitan? I can understand that some screwed up systems have problems after an upgrade. But we are talking about clean installs here. So please Apple - don't tell us about restarting routers  - just do your homework  and please fix this BUG in 10.11.2....

In my original post, I complained about OS X El Capitan losing speed after sleep.  For example, network speed would drop from 48Mbps to 24Mbps.  Never could find any solid reason after discussions and assistance from Apple Support.  The only interim solution for me is to just click on the little Wi-Fi radio symbol on the right top bar and shut off Wi-Fi.  Wait a few seconds and then turn it back on.  When I test the speed after that it is back to normal.  No need to shut down Safari or anything else.  But it would be very nice if this didn't happen.  I'm guessing there's a Wi-Fi bug somewhere in El Capitan.

I am facing the same issue with slow WiFi on my iMac and Macbook both running OS X El Capitan!

Just found the solution for iMac:

My network consists of Apple Time Capsule and additional Apple Extreme as the wifi extender.

Once Extreme is on, the WiFi speed drops 5X (my internet download speed if 50mb) so downloading comes to 10mb.

When the Extreme is OFF the speed is full.

No luck with MacBook Pro, so I hope the fix will be out soon!

Just set the wireless mode on your router to N (802.11n), and not AC (802.11ac). It worked for me..
There must be some bug on el capitan that makes the connection really slow if connected to a wifi with its wireless mode on AC.

Hope it works for you too..!

Yet another release with Major problems! This is total crap. I don't have time for this. My computer is totally F-d up now. I'm not just surfing the net. I have work to do. Ugh. The quality control at apple is in serious decline.

I just wanted to put this out there.... I was experiencing slow wifi speed after updating to El Capitan. I confirmed this by using speedtest.net on my iphone (IOS9) vs my IMac(now El Capitan). Iphone saw 27Mbps and imac saw barley 1Mbps. I noticed that my wireless router was using channel 6, So I switched to use channel 11 instead and instant speed was restored.  Not sure why this made a difference but it did. I now get consistent speeds over 25Mbps using speedtest.net.

I did scan my neighborhood to see if Channel 6 was over utilized in the area, but it was not. Channel 1 and 11 were more common, so channel 6 seemed like it would work better....

Either way, my speed is restored...

Also to note that I still have issues with my wifi reconnecting after the imac was in sleep mode..... Annoying...

I have exactly the smae problem

apple genius bar couldn't help

As part of your troubleshooting, try creating a new account and connecting from there. That's what I did and it solved my issues. I never really got to the bottom of exactly what was causing the slowdown. So ended up bringing all my BACKED UP data over into the new account. Good luck. There is a solution.

I am not sure what you mean by creating a new account??  Can you explain as I would be willing to try it.

Where do you change the channel??

You will need to login into your wireless access point/router and modify the wireless channel setting manually.  This should not be necessary for most users. I manually changed the channel to channel 6 a long time ago with some intent. To see what channel your running on currently: Hold down the "option" key and select with mouse the wifi indicator icon in the status bar (upper right corner). You should see more information about the connection you are currently on, including the channel.

It is possible that just switching channels, regardless of the channel, actually fixed mine.

I'll see if I can figure this out.  Thanks.

Yes, create a new user account I mean. Apple > System Preferences > Users & Groups.

From there you should be able to create a new user account. Then login to that account and test your connection.