Really unless I misunderstand, you must have a wiring issue that is allowing a path for DC positive to ground, this may have been as a result of your Solar install, but it is not due to Solar, there is nothing inherit about Solar that would cause a current
A way is to turn every thing off, so that nothing is drawing power, then disconnect and measure the amperage draw from the batteries by inserting a multimeter in line with the positive cable, if there is any current
, start disconnecting circuit breakers till the current draw goes away, then you have found the circuit that may be the problem, of course some circuits draw a tiny bit of current to keep clocks set etc., too.
Or hire a an electrician to find your leakage, there are ways to measure it to that a Marine
electrician may have, a reference electrode I believe its called, but the "leakage" can be measured, and or determined if you have a problem or not.
On edit, read this