they take longer to establish in salt water, up to 6 months for cold salt water tanks
so blackish or is that brackish will take longer than fresh
if blackish, as henward posted ph will affect their establishment
not quite 10k
had a gravid female too when they were taken
very sorry saga all round just to teach a suspected smuggler a lesson by the authorities
amazing how due process can be twisted
not smelt or yellow eyed mullet
possibly grey by the shape
a lot of bait fish are being chased inland by kahawai etc at the moment
http://www.niwa.co.nz/our-science/freshwater/tools/fishatlas/species/grey_mullet
don't just take out the top half of substrate as this is where your bacteria is mainly
you may just expose a slightly more anaerobic layer
may just be better on second thoughts to take it all out by syphoning
then do water changes over next week or so
keep an eye on your water parameters
yes it would be worth it just to see if that is the problem
i have always been a fan of substrate but run with none now
if you have fauna that turn it over it is good
but without, it can be an organic waste trap
remember when you remove it you are changing the balance of bacteria in the tank
preheat some new salt mix for water changes afterwards
personally i would remove 1/2 the substrate then the other 1/2 a week later
how long since the tank was set up?
and does it have coral rock in it?
or just rock from the beach
there are no short cuts for the long life of a marine system
are you filtering your own top up water or buying bottled water
your system could do with a skimmer
and how often are you cleaning the top filter on the tank
not a great fan of using the top filters for marine i am afraid
you have a low bio load which is good
do you test for magnesium?
so long as it is alright to use on polystyrene it will be all right
no matter how good your undercoatings are there will be small holes the resin will get through and eat away the poly underneath