William, Its a 12v system of 6 x 2v cells that are 18 months old, 60A 3 stage Studer charger, 360 watts solar & AirX 400 watt turbine. I rely solely on solar controller to equalise which occurs every 30 days approx. but noticed after your tip they were equalising for 3/4 days! I moved the weak cell some time ago but to the negative terminal, I will change that to the positive as you suggested. I've been running a desulphator for 5 months now & realise its a slow process but well worth it. Water levels are going down equally & voltage readings show a difference of 0.02 but I dont think my multi meter is that accurate. I'll try sg readings after 2 hours of rest.  
Thanks so much for your advice.
Paul