Before you go investing in solar, I would find out the culprit if that huge increase in your electric bill...unless there some sort of malfunction, there's no way your tanks would result in an increase of $350.
Below is a breakdown of the monthly cost to run what you listed, using PG&E's highest tier of $0.36/KWHr:
Two XP4s - $16.08/month
Eheim III- $7.78/month
25W UV- $6.48/month
36W UV- $9.33/month
1200W heaters- 38.88/month (assuming they come on 3 hours per day)
The equipment you listed only draws 218KWHRs/month, which comes out to a monthly total of $78.54 to run.
Unless you are running 1,000W Metal Halide lights that you didn't mention, there is something else drawing lots of juice.
In order to see an increase of $350, you would need to use an extra 972KWHrs! That's the equivalent of running a device that draws 1,350Watts, 24/7!
I would contact PG&E and have them do an energy audit...I believe they will do that for free.
I feel your pain...PG&E rates are some of the highest in the country...the rates are ridiculous.