At ACP - General - Board Configuratuon - Post Settings, we've a number field for Topics per page that supports min="1" max="9999" aka int:1:9999 (found on includes/acp/acp_board.php), and at ACP - Forum - Topics per page, we've min="0" max="9999" (Found on adm/style/acp_forums.html). 

Those values should be equal, but thats not why I created this ticket.

The 1st one is saved at phpbb_config table, on config_value column, and that's a varchar.
On the other hand, the 2nd one is saved at phpbb_forums, on forum_topics_per_page column, as we can see on /includes/acp/acp_forums.php > 'forum_topics_per_page' => $request>variable('topics_per_page', 0),
and: array('lang' => 'FORUM_TOPICS_PAGE', 'value' => $forum_data_ary['forum_topics_per_page'], 'column_type' => 'TINT:0'),
and on phpBB/phpbb/db/migration/data/v30x/release_3_0_0.php 
we can see too: 'forum_topics_per_page' => array('TINT:4', 0),

So basically it's a TinyInt __ instead of a varchar. And when on ACP - Forum I try to put A value for topics per page as 200, I get an error saying the value its to high, and I should use a maximum value of 127.

This should be fixed, since I can put globally at 200, but I am not able to do it per forum settings.