HI
The growth of Briopsis showed you a problem in the nitrogencycle, you have areas where is a shortcut in the cycle and there will be produced No2. This is what the Briopsis want. You need to stabilize the nitrogencycle on that way that you add Nitrate. The problem you have is that the maesurement of N03 in seawater is extremly difficult and will be affected by the No2 in the water to showed wrong test levels. If you raise up the Nitrate level ( only over Sodiumnitrate ) you will see that the briopsis will gone and your system stablize much better. At the same time you need
to reduce your TraceElements in the water , best way here is to use a handfull Zeolith.
Also stop or reduce adding Carbon Sources and or bacteria products till the system is stabilized.
The problem of not balanced CarbonSources is that they can limited the work of the nitrobacter group which will brings then this results.
Rgds Claude
* sorry for my bad english i write from Germany please feel free to ask if something is not clear enough