fridmani1

I can't tell from here what killed your corals and snails but I doubt it is Old Tank Syndrome, I don't even think that exists. Snails are hard to kill but the only thing that will kill them fast is some type of metal poisoning which will also kill your corals. I wouldn't know how a metal like copper could get in your water but it will kill inverts while leaving fish alone for the most part.
While you had your algae spurt I would not have used any type of chemical to eliminate it or the phosphate, I am leary of chemicals that remove other chemicals.
I do however like algae to be used to remove chemicals and maybe even metals.
I would have let the algae grow until it used up all the nutrients, then it would have started to die and it will die very fast. At that point I would have used a canister filter like a diatom filter to quickly remove the dying algae "without" changing water. Let the algae remove whatever is in your water, then remove the algae. "Then" change water after all the algae is gone.
Your water, or your phosphate remover may be adding something to your water that would make it tough for corals and snails.
That is my recomendation, but Like I said, I can't see your tank from here.

I have a few questions if you don't mind. How long has your tank been up and running? what is the total volume of water including sump? how often do you do water changes? what is your water change percentage when they are done? how old is the rock? since pulling the rock from the tank have the phosphates shown decline in the tank? do you have a sump? and if so do you keep it clean or does it have detritus building up in it? do you have a RO-DI unit? when were the filters changed in it last? have you tested your source water for phosphates?

I agree with paul.

Thanks for the responses; I should have provided more back-ground.

I will post more to the blog with some pictures. (I can't figure out how to post pictures in comments)

For now: Tank is 150 Gallons + ~40 gallon custom sump from Melevsreef. I typically do a 40 gallon water change about 1 a month.

The tank and sandbed + plenum are over 10 years old. The liverock was changed out around 2 years ago to get rid of a mushroom plague. I got the rock from Coral Universe as a trade for the mushroom rock. I'm guessing he had the rock there for a while before I got it.

The Phosphates in the tank have not reduced much despite pulling back on feeding and with the phosphate RX. I also have a refugium with caulerpa that is growing well. I do have a filter sock running but I keep the bottom of the sump clean. In the refugium I have a sandbed as well.

I have an RO-DI and I've tested the water for phosphates and it reads 0.02PPM which is pretty good.

I'll post pictures on the blog tonight to show what I'm talking about here.

Like I've said I've had the tank for over 10 years and never had a die off like this. Especially the snails it's a big mystery to me so that's why I'm thinking about the total tank tear down. And since it is been up non-stop for 10 years thinking I have Old Tank Syndrome.

I gotdd

I would say start doing some large water changes maybe twice weekly to try and dilute what could be ailing your inhabitants. Run some fresh carbon and change it out 1-2 times a week with a fresh batch. I would try running a phosphate bad if you have a place that all your water runs through. instead of using phosphate x maybe you can switch over to vodka dosing, you should have more long term success with that I think.

If you are not running a DSB I think I would look under at the bottom of the sandbed to make sure you have no black sand deposits before changing your sandbed, if that gets disturbed it can wipe a tank (in fact check for that anyway) if you do have that problem I would suggest pulling the inhabitants of your tank, and and corals out then draining the water out before getting all the sand out to change it. then while your at it give everything a good scrub down and replace it with new sand and either new rock or cured old rock and you will have hit the reset button .

Do you have any rotten egg smell coming off the water or did you bury live rock during the last new live rock additions?

I don't have any rotten egg smell and I didn't bury any rock in the sand. Now the sand I have is very large grain (so it would be more accurate to call it small gravel).

I have about 3" of the "sand" above the plenum. The sand that I used is the following: http://premiumaquatics.com/aquatic-s...C-RSAND40.html

I'm thinking of using the Tropic Eden Mini-Flakes or Reef-Flakes and eliminate the plenum. I'm going for a 3.5"-4" sand bed.

When you have higher PO4 levels in your tank, it does get into the sandbed and rocks. My 280g was loaded with PO4 back in 2004-2005, measuring 3.0 ppm. I used a lot of GFO products with less than stellar results. Phosbuster Pro and Phosphate Rx both work great though. Each time you treat the tank you knock it down, and the rock leaches out more. Eventually the rock will empty out, especially if you are "cooking" it. To cook it properly, you've got to shake the rock strongly once a week, and move it to a new barrel of saltwater, tossing out the old water and detritus. Skimming can help, but I've never bothered. The rock you are cooking now, and using Phosphate Rx.... how are you exporting the flocculant? Skimmer? Filter sock? Nothing?

It could be possible that the plenum is wiped out or damaged. Do you still remove some fluid from that zone from time to time? The dying snails will add PO4; did you smell them as you pulled them out? Check for stray electricity. Also if your Mg is too high, snails don't do well.

Thanks Marc,

I've not been changing the water that often in the barrel. I will start now. The water in there is still at 0.2. When I dosed the Phosphate Rx I didn't remove the flocculant. When I dose the tank I would turn off the main pump - dose in the skimmer chamber of the sump and use a cartridge filter to circulate the water. But for the cooking barrel I didn't bother. I'm going to change out to GFO moving forward for the cooking rocks.

As for the dying snail yes they smelled bad. I checked the Mg tonight and it is 1320 so seems fine.

How would I check for stray electricity BTW?

I've never actually pulled any water from under the plenum for the life of the tank. Didn't think you were supposed to disturb the area. Before I tear it out I'll pull some out and do some tests.

Do some research. I read years ago that you are supposed to draw a little water out of there from time to time, IIRC.

Dying snails add PO4 to the water. In spades.

Here's the article about stray electricity testing: http://www.reefaddicts.com/content.p...ay-Electricity

I've always dosed my tank at night, and let the skimmer export it overnight. The next day the water is clear, the livestock is happy, and the test measures 0 ppm again.