Zoanthids Receding

[gigmeyer]

I bought a small zoanthid colony last April that grew out of control up until the September/October timeframe. Right around that time, I was considering having to find a way to control its growth to prevent it from taking over the tank. Since that time, it has been slowly receding and I'm concerned it will disappear altogether within the next few months. The polyps that remain all appear healthy and all my other corals are very healthy as well.

One change during that timeframe was lowering the photo period from 8.5 hours to around 7 hours as hair algae has been an ongoing problem. I've also been dosing with Magnesium (Kent's Tech-M), but have backed off on it significantly over the last few months as the hair algae is now very manageable.

Today I'm increasing the photo period from 7 to 8 hours to see if that helps the zoanthids without causing a hair algae problem. The light is a Sunpod 150 HQI with the original bulb that is about 14 months old.

Has anyone experienced this problem or have other suggestions on what might be the cause?

Thanks

 

[Colin_T]

Assuming the water quality is fine then it could be old globes. Over time the quality of light coming out of globes decreases and this combined with the shorter photo period could be causing issues. However, if the corals are still keeping good colour then it is unlikely to be light. Poor quality light, or low lighting levels will cause corals to fade and eventually bleach (go white due to loss of symbiotic zooxanthellae).
I would be inclined to thinking it is water quality related. Have you done any water changes in the last few months? If not perhaps do a couple of big water changes and see if that helps.

 

[SkiFletch]

Actually Gig, I'd be more inclined to worry about predators. Zoanthid eating nudibranchs, sundial snails, or something else could be slowly picking off your colony. Could have hitch-hiked in on a different frag you added. Your light is more than adequate and as Colin said, the zoas would change color before dying to show you their lack of light. Chemistry problems are unlikely, as they will manifest themselved as closed up heads. The only thing that makes sense is predation and/or nearby coral aggression. What are the other livestock in the tank?

 

[steelhealr]

I agree with Ski.....in that...could be coral aggression. What other corals are in your tank. Personally, I don't think that reducing the lighting interval is the best choice when it comes to taking care of hair algae. I believe it's a water problem vs. lighting. I would bump the lighting back up slowly and see how you do. Do you have a refugium? SH

 

[gigmeyer]

Thanks for the input guys. I haven't seen any signs of predators, but did see one of my newer emerald crabs picking away at the colony some last evening. The hermits crabs have been regularly trespassing on the colony as well. There aren't any corals near by except for a green open brain coral that has been there since last July. This has been going on so long that it's hard to tell exactly when it started, but it may coincide with using Reef Tech-M. I've cut that so far back that my last Mg test was under 1300 from a high of about 1500 when hair algae was a problem.

I don't have a refugium at this time. This is the 2 compartment 24g model, so I don't have the third compartment in the middle that you use Steele. I just use Rowaphos, Sea-Chem, and activated charcoal as well as a filter pad over the intake replaced weekly. Nitrates tend to vary between 5 and 15 with weekly 4g water changes. Occasionally I'll do an 8g change to knock them back more. The one time nitrates hit 20, my red lobo immediately looked unhealthy, so I figure it is my guide for nitrate problems. I've thought about a small HOB refugium in the past, but haven't done anything about it as I like the simplicity of this setup and it's been pretty stable.

Livestock at this time are:

Snails: 2 Nassarius, 2 Cerith, 3 Nerite, 2 Zebra Turbo (new)
2 Emerald Crabs, 1 Skunk Cleaner shrimp
For hermits I have several scarlets, one zebra, one blue-legged.
Known hitchhikers are peanut worms, collonista snails, and feather dusters.
All other hitchhikers seemed to disappear fairly soon after adding the 6 line Wrasse

Feeding is about 3-4 times a week. I vary between mysis shrimp, brine shrimp, and a mixture of flake food and pellets.

Fish and corals are listed in my signature except for a small montipora I swapped half my brain coral for and a really small galaxia that just appeared recently. Both of these were introduced after the problem began. I fragged the brain as it was growing out of control too and I originally thought it was the causing the problem.

Are there some predators I should be specifically looking for? Or is it possible the crabs are working on the zoas due to lack of other food?

 

[steelhealr]

Zoos are pretty tough characters and I would bet my money that it is either water quality (presence of hair algae) or lighting interval. There is one way to find out..and that is bump up the lighting interval and see. I didn't notice but do you test for phosphate? SH

 

[gigmeyer]

Phosphate is one of the few things I have never tested for. I do use Rowaphos and a phosphate reducing pad replaced weekly over the filter inlet, but that doesn't obviously guarantee anything. The hair algae is minimal at this point. My plan is to work on reducing nitrates with larger water changes as they have spiked a bit (15-20 ppm) and the lobo is starting to show signs of stress. Will replacing the activated carbon and Rowaphos help here? It's been about 3 months since the last change.

 

[steelhealr]

I change my inserts every 3 months. Some say they can go 6, but, that's why this is an art sometimes. I don't use activated carbon in my tank but....I DO use ChemiPure (looks like it to me). SH

 

[SkiFletch]

Well, going on the predator route, the three most common Zoanthid predators are Zoa-eating Nudibranchs (very small ~1-2mm and diurnal), Sundial Snails (also small ~2-4mm and mostly nocturnal), and finally Zoanthid spiders (slightly larger ~5-10mm but nocturnal). Emerald crabs usually aren't predatory towards Zoanthids, but their constant probing of the rockwork for algae will end up on the bodies of the Zoas and will slowly irritate them, perhaps to death.

With a 150watt halide on a tank as small as yours, I really don't think your problem is lighting. Increasing the photo period won't hurt, so it's worth a shot, but my guess is likely a predator and possibly water quality.

 

[gigmeyer]

I went back to my pictures from January 20th (1 yr anniv!) and the zoanthids looked pretty healthy back then. Around that time, I had separated the original colony from the growth that had spread to my largest tonga rock in an attempt to create 2 colonies in my tank. I also added 2 emerald crabs to replace a crab I lost in December after a 50% water change to reduce nitrates. Both colonies have suffered hugely since then, yet everything else remains stable and healthy. Could breaking off the original colony have started this problem? At this point I'm just going to let nature take its course, but if the crabs may have irritated the colonies somehow through foraging, I wouldn't try to start again with zoanthids.