stability by seachem. its bacteria in a bottle.
Vodka didnt work? your probably nitrate limited.
If your nitrates are undetectable you may not have enough to get a good bacterial population going.
This may sound crazy but adding a little potassium nitrate may be the ticket to getting your phosphates down lower.
Prodibio works because it feeds bacteria carbon. These bacteria then consume the carbon, nitrates and phosphates. If anyone of the three are limited (not available in large enough quantities) then these bacteria die off.
So If you start out with low Carbon, Low Nitrates but high phosphates then you can see what happens. Over time the nitrates are all used up but theres still too much phosphate because you started out with an imbalance. You can add carbon(vodka,prodibio,methanol,ethonol,sugar,snickers bar

too your hearts content but it wont be utilized.
This is typical of systems that run deep sand beds. The DSB is good at removing nitrates threw DEnitrification but doesn't address phosphates. So over time the tank becomes imbalanced.