Potters eating my pincushion urchin?

[MRRBW]

I woke up this morning and went to look at my tank first thing as always and I see my urchin on the front glass looking like the photo below. It took a sec to register and a few second looks. 5 minutes later I see my potters picking away at the urchin. Couldn't believe it. Has anyone seen this before? Is the urchin grave danger? The body surface of the urchin is intact, it's just missing the spines from about 3mm and up.

 

[KJ]

Look like your water chemistry its of.
Tell us your # Amonia NO2 NO3 Mg CA Alk Salinity

 

[MRRBW]

Not sure why you jump to my water chemistry is off. Have an explanation, I don't see the correlation?

Look like your water chemistry its of.
Tell us your # Amonia NO2 NO3 Mg CA Alk SG

 

[KJ]

If your sea urchin is losing spines , there is usually something wrong with your water chemistry , I don`t mean to offend , I am only trying to help you, it doesn`t have anything to do with the angelfish

 

[MRRBW]

no offense taken, just didn't see the two related. I also saw my potters picking at the urchin. I assumed it was strictly the potters fault

If your sea urchin is losing spines , there is usually something wrong with your water chemistry , I don`t mean to offend , I am only trying to help you, it doesn`t have anything to do with the angelfish

 

[MRRBW]

So I tested the water, honestly haven't done it in months. Little surprised with the results. Only two that jumped out at me were the KH and the salinity. I was surprised because the nitrate and phosphate read zero - which I have never had. Phosphate reading is taken in stride as I have algae growing all the time and is a constant battle to clean it out of the tank. Tank is 15 years old, as is the sand and rock in it. Not sure the results of the water tests would equate to the urchin losing spines though, unless the kh is responsible, but everything else in the tank is doing fine. I added some reef builder to get the kh back up to where it should be. Probably going to take a week or so as I don't go for quick changes.

 

[MRRBW]

Okay, so after the water testing yesterday, it made me think of what was causing the spines to be missing from the urchin. Well, just now I saw my potters going to lunch on the poor guy. I'm pretty sure this is the source of the problem. I'm feeding the fish 2-3 times a day and there's enough algae to munch on. Has anyone else seen this before?

 

[FarmerTy]

Maybe I missed it but Potters angel or wrasse?

 

[MRRBW]

Sorry, don't think I mentions that, but it's my potters angel. He's becoming a bit of a pest. But I adore this fish. It's becoming love hate I think

 

[eatbreakfast]

Low kh can have a major impact on urchin spine strength and production. The spines are made of calcium carbonate after all, the carbonate is what is added in dosing alkalinity supplements. Angels are ill equipped to damage healthy urchin spines, but weakened spines are another matter.

So the water chemistry inquiry was valid and likely where the solution lies.

 

[MRRBW]

Well, I think the kh may have been the culprit. Can't think of anything else. The urchin unfortunately has not made it. It stopped moving last night and I saw it ejecting its innards from the top this evening, so out it came from the tank. The bristles definitely felt off, almost too soft and very very brittle. I brushed my hand and a section came off. I've dosed 2/3 days reef builder. Today after just one dose the alk went up to 7. So one more dose today. I'l keep testing it every 2 days until I get back to 10 where it was before. Lessons learned the hard way I guess. Thanks guys for the guidance.

 

[jetmaker]

The angel is most likely eating film algae