I'm using Joomla 3.62, Gantry 5, Hydrogen template (customized) on a major web site hosting service, which has control panel and phpmyadmin.

I installed K2. Then the template's swiffy animation (developers.google.com/swiffy) in the template quit working and disappeared.

I uninstalled K2.

I noticed that mysql database had increased in size by 50%.
I tried to optimize mysql and received the following error.
Fatal error: Cannot redeclare pma_tableheader() (previously declared in /www/public/phpMyAdmin-3.0.1/db_structure.php:81) in /www/public/phpMyAdmin-3.0.1/db_structure.php on line 116

I ran a mysql checktable and received the following errors:
Problems with indexes of table `tbl_user_keys`
The indexes series and series_3 seem to be equal and one of them could possibly be removed.
The indexes series and series_2 seem to be equal and one of them could possibly be removed.

At this point, it looks like I'll have to do a completely new install of the website. Fortunately, it's a test site.
The test site is Fraudstoppers.com, although I don't know how long I'll leave the broken site up.

I note a post at Github.com in the Gantry 5 project .
mahagr commented on Jul 8
I'm not able to get K2 (v2.7.0) to work:
Fatal error: Class 'K2HelperHTML' not found in /home/matias/www/joomla/administrator/component

I'm interested in the experiences and advice of other people regarding K2 with Gantry 5.

I have not used Gantry 5 but the issue with Swiffy is most likely a JS conflict.

If you experience it again, send me a link so I can take a look.

Fatal error: Cannot redeclare pma_tableheader() (previously declared in /www/public/phpMyAdmin-3.0.1/db_structure.php:81) in /www/public/phpMyAdmin-3.0.1/db_structure.php on line 116

Are you using an obsolete version of phpMyAdmin?

Info update:

1) Swiffy Animations -- I think you are right that K2 and Swiffy animations have a Javascript conflict. When both are installed they may cause a recursion problem. Later, I found out that this also happens with Swiffy animations and Rockettheme's Roksprocket extension. My solution is that I just cannot use Swiffy animations with certain Joomla extensions.

2) Fatal error: Cannot redeclare pma_tableheader() -- I now believe that this a bug in myAdminPHP. I posted the issue in Github. github.com/phpmyadmin/phpmyadmin/issues/12558 . I also opened a support ticket with my web hosting service to update their version of myAdminPHP.

3) "Problems with indexes of table `tbl_user_keys`
The indexes series and series_3 seem to be equal and one of them could possibly be removed.
The indexes series and series_2 seem to be equal and one of them could possibly be removed."
I followed the error message's advice and dropped table rows for index series_3 and series_2, which solved the problem.

Summary:
In my initial post, I assumed that all of these issues were caused by K2 because I had just installed and uninstalled K2 when I noticed the problems.
Now, I think that it was just coincidence, and I apologize for putting the blame on K2. If you concur, we could marked this issue as resolved. Thank you for replying and helping.

Thank you Pinto you mentioning this :)
I really appreciate this.