Will setting my Joomla site to offline mode affect my SEO?

[responder5]

under construction websites will be put back as there are many developed websites to compete.

regarding putting a website to maintenance mode will not really hurt the website but it depends on how long you will put the website in that mode. Even google itself do the maintenance job but they select very less traffic time to do such things and moreover they inform their users ahead of doing it so it's an informed thing and not something like on and off when they want.

Regarding loosing rankings yes you will loose when google finds your website is under construction. but if you put a website to maintenance mode for some time (cpl of hours) then that should be fine.

When you put your website back and promote well and has quality content then you will slowly start seeing you site in search engine rankings for your targeted keywords.

last but not least, if you have no competition then don't even bother asking this question because you can get rank faster when you site is live and ready.

Your "melodica forums" (with quotes) keyword has very less competition in Google, hardly 443 page results