Well, the bad news now is that you have 2 gobies, not just one---infauna predators. The really bad news is the green brittle star. See if you can get him out of your tank [yeah, right]. He is a fish predator. Very pretty and cute when small, and a great detritivore, however, once mature [which doesn’t take long] the green brittle will become the “jaws” of you tank. Get him out if at all possible. Any other brittle star would be fine, but this one is not. I know, they are very pretty, aren’t they.
Well, by playsand, I’m assuming that you don’t mean Southdown do you? Happen to know what the content of the sand is? Probably silica based. How fine are the grains? Take a good look at your DSB through the fish tank glass. Use a magnifying glass with a good flashlight. Is your sandbed stratified? Larger grains of sand top layer, with stratification occurring every inch or so to smaller sizes of sand? If so, then you have grain size diversification which a good thing. [By chance, do you recall ever seeing bubbles form in your DSB when it was new?]
As I thought, you establed good water movement at the top of the tank and none at the bottom. You need to correct this by either placing some PH’s down at the bottom or running spray bars down there or inlet/outlet tubing with pumps elsewhere---but something.
BTW: With all those predators in the tank and you not allowing the detritivore kit to multiple prior to adding fish, then you are going to need more kits. Your sandbed needs to be well populated. You should be able to see stuff crawling around on the sandbed and in and out of the rocks. Hopefully you have some fire [bristle worms], do you? These guys will dig down into that DSB and give it a good working over. Excellent infauna in spite of their “bad press”.
Contrary to popular belief, you do not feed a DSB system less food...you feed it more. However, in this situation where you have such high nitrates, you need to take care of that problem. Keep in mind that your fish are always looking for food, though; if you don’t provide it, then they will get it elsewhere [like the organisms on your LR or LS??!]
Do look at the new, bigger version of the prizm and see what you think. Don’t get the little original prizm, its good for a 20gal or a hospital tank, but not for your tank [don’t go by manufacture’s ranking, as they overrate skimmers on capacity]. Again, take a look at the Remora and the prefilter option. For your setup with all of its predators, this could be a viable option for cultivating pods and additional snails, etc., without having to think about adding a separate ecosystem outside of the tank.
Take out the filter pads in that filter, just leave the filter on to circulate the water. Alternatively, you can change out those pads weekly, but then that can be a rather pricey expense for a poor choice of filtration. Once a week, if you want, you can add some carbon pads to your filter, and let it run for 24 hours---at least until the nitrate situation is under control and you tank’s LR and DSB gets up to grade.
Don’t stir or vacuum your DSB. If it is dirty, then leave it dirty. The action required is to build the infuana population, not to place Band-Aids to conceal a problem.
I’d suggest:
Go to Red Sea’s and AquaC’s webpages and check out the skimmer options then get one.
Think about what you want to do to get more water movement at the bottom of your tank. [The easiest thing to do is to add a couple more PH’s].
Ditch the filter pads or start replacing them weekly until you get the skimmer, then ditch the filter system altogether.
Think about the adequacy of your system’s sandbed and live rock fauna. Using a magnifying glass, can you see lots of these organism all over your sandbed and crawling in and out of your LR? Worm, worms, worms make the best infauna for the DSB. Do you have fire worms? These are the pink/lavender bristle worms very common to tanks with live rock. The fighting conch is an excellent choice. How big is he? How’s diatoms in your tank? Do you need more detritivores?
Anyway, glad to help! Keep us posted on what you decide to do.