Rectifying a responsive issue on Joomla website when viewed on ipad/iphone

New Joomla site which was based on a commercial template base and then customised - has already been launched, however we are having difficulty getting the site to render correctly in an ipad/iphone in portrait orientation only. We do not want the site to be typically responsive ie to render differently on small devices , we simply want the site to appear at 100% width of the device in any orientation and allow the user to zoom in as required. The site currently displays wider than 100% available width on ipad/iphone devices at portrait and cannot be zoomed down to show full width. The site is viewing correctly on all other devices/resolutions etc . The solution is likely to be in tweaking or adding CSS settings for these specific devices or it could be a template issue but we have had difficulty finding the solution. The ideal person we seek will be able to suggest css changes without requiring full access to server/site, allowing us to make the changes and test and ensure the changes do not affect other devices/resolutions.