Unfortunately, March might be the worst time of the year to dive California. We've had a wet winter so far, so there are lots of nutrients washed into the water and the longer days mean the algae goes nuts -- we can get green algae blooms and red tides around this season. At the same time, the water is still pretty cold (mid 50s is typical) and hasn't started to warm up yet. A good 7mm fullsuit with a hood or hooded vest is minimum for most people.
Having said all that, sometimes you can get lucky and find some clean water (15'+ would be a good day off the beach) and if you can get out to the islands (Catalina or the Northern Channel Islands off Ventura) you might get twice that visibility if you catch it right. Hopefully there is some kelp around this year (we've had warm water last few years and a rough winter, both of which are bad for kelp, but it grows fast and you might get a chance to dive in a lush kelp forest).
If you want to dive the islands, you will need to be here on a weekend (hardly any boats going out midweek these days). There is an option to take a ferry to Catalina and dive the Avalon dive park but it's a lot of work to schlep your own gear and ends up costing almost as much as a charter boat (generally about $150-$200 for 3 dives).
Given all that, if you are gung ho for a dive, DM me your dates I will look into options and let you know what I can find that is available.
