Odd spongey algae growing where zoa's died off

[mattd017]

So, I had a really bad bubble algae problem. Couldn't keep up with it with manual removal and a clean up crew wouldn't work in my tank (20 gal, emerald crabs would be eating muly coral in a week). So I finally dosed reef flux. It worked for the most part, some still hidden in crevices, but it's about 95% gone. Then, suddenly, about 3 weeks ago, I saw something that looked like cyano. Which I ignored cuz I assumed it was just slight imbalance from the bubble algae die off. Turns out it was dinos, prorocentrum to be exact. And in the course of about 3 days, it covered everything and started killing off my softies. Hammer is dead, 90% zoa's died, mushrooms barely hanging on, pipe organ gone, Xenia on the struggle bus. Surprisingly, my SPS and LPS are totally unaffected. I'm starting to get ahead of them by dosing NeoPhos, Silicates, run a 9watt UV and my skimmer from lights out to lights on, dose beneficial bacteria and algae first thing in the morning. Diatoms are showing up in my samples and dinos aren't everywhere, just almost everywhere.

Here's where my question comes in:
Where my zoa's died off, a strange spongey greenish yellow algae has been growing in. It crumbles when you pull at it with forceps. It has chlorophyll but also looks like it has the sharp diatom make up. I have no idea what it is and it seems to be choking out the few zoa's I have left. Any ideas? Thanks!

 

[ISpeakForTheSeas]

That is 100% a sponge (great microscope pics of the spicules by the way). Generally, sponges are harmless, but some are invasive (not necessarily harmful, but they may be if they grow over the polyps of corals and smother them), a few are chemically harmful to corals (they beat corals in chemical warfare for space on the reef), and a very small minority are both.

If the zoas open like normal in patches where the sponge isn't (or close once the sponge grows closer to them), then it's outcompeting the zoas chemically - removal would be necessary.

With regards to it growing around the base of the zoa polyps: as long as it doesn't grow up and over to cover and smother the polyps, it's not harmfully invasive with its growth - many sponges can grow around the base of corals like you see in your pics there without causing harm. If it starts to grow over the polyps themselves (not just the base/stalks), then it's harmful and should be removed.

For removal if wanted/needed:

The best way I've heard to control sponge growth at this point is to use a steel straw to scrape and siphon out the sponge you want to remove. Sometimes you can create bad conditions for them and kill them off that way, but that's typically much harder and not always effective.

Some other sponge removal methods:

Other suggestions include exposing the sponge to air (obviously not a guaranteed solution, and definitely not viable for this situation); hydrogen peroxide dipping the sponge (again, not viable here); injecting the sponge with hydrogen peroxide, vinegar, boiling water, or air; microbubbles in the display; and a few more. Predation is not usually a good solution for this issue

Basically, if the sponges have enough food and enough trace elements (which for most sponges includes silicates) to meet their needs, then you’ll see their populations booming.

If you can figure out what’s allowing them to thrive in your tank, then you can deal with that root cause and get rid of them.

Some people may suggest scrubbing with a soft toothbrush to try and avoid irritating the zoas.

Also, with regards to the zoas:

Yeah, if you do scrub it off in a bowl of tank water, since it's growing on palys, you may want to run carbon in the bowl to absorb any toxins.

 

[mattd017]

That is 100% a sponge (great microscope pics of the spicules by the way). Generally, sponges are harmless, but some are invasive (not necessarily harmful, but they may be if they grow over the polyps of corals and smother them), a few are chemically harmful to corals (they beat corals in chemical warfare for space on the reef), and a very small minority are both.

If the zoas open like normal in patches where the sponge isn't (or close once the sponge grows closer to them), then it's outcompeting the zoas chemically - removal would be necessary.

With regards to it growing around the base of the zoa polyps: as long as it doesn't grow up and over to cover and smother the polyps, it's not harmfully invasive with its growth - many sponges can grow around the base of corals like you see in your pics there without causing harm. If it starts to grow over the polyps themselves (not just the base/stalks), then it's harmful and should be removed.

For removal if wanted/needed:

Also, with regards to the zoas:

I initially thought they were sponges, but I guess I never realized they could be photosynthetic, so assumed they were some sort of algae. Them booming now makes sense since I'm running silicates around 5ppm for the past week and a half. It doesn't look like there's any good sponge ID keys out there, so I don't know if they're super harmful and if they'll recede once the dinos are gone and the silicates get used up. I also don't know if they're choking out and harming the zoas or if they're just taking advantage of the zoas dying off from the dino poisons. It's nuts this tank has been going for 2 years and had 0 issues until 3 weeks ago and now I've lost so many of my corals (not to mention the time and money down the drain, literally).

Thanks for your ID.