How old is your battery bank?
How budget conscious are you?
Are you about to go on a long voyage away from chandleries?
After fully charging how long and how many amps does it take to get to 50% charge measured by specific gravity?
Assuming that the answer to the last question is acceptable and:
Assuming you really want to maximise the life from your battery bank. I would consider disconnecting the two worst offending batteries. So your bank is 10 batteries wired up as pairs to give 24v. Then see how the rest of the bank performs. If the remaining bank holds it's charge well then you must decide what to do with the two dead ones. Maybe equalise/replace them or do without.
As for equalisation. You could try it before changing the dud batteries. If you fully charge the bank with your Dolphin chargers until they accept no more charge and then turn all load off and on a sunny day use the solar regulator to equalise. The batteries should gas and boil, this stirs up the electrolyte and hopefully cleans off the plates. One hour is not enough you could reset it several times.
The main advantage of wet cell batteries is that you can boil them and refill with distilled water.
Nick Amelia (54) with a new bank of Lifeline AGM, new chargers as the old Dolphins died and 530w solar and two wind generators.