Coral Disease

[mousefish]

I have been keeping marine aquaria for more than 20 years and have occasionally had problems with marine disease but never to this current extent. Over the past two years, I have periods where some of my montipora species are affected with an RTN type condition, but they have always grown back. In the last 6 months however, something has been affecting multiple types of corals in the tank including Acropora, Duncanopsammia, Blastomussa, Caulastra, and Favia species. Nearly every coral in the tank has stopped growing but the fish seem unaffected. Other inverts such as shrimp, snails, isopods, etc... all seem fine as well. I strongly suspect a viral or bacterial infection but there may also be an overlooked water quality issue (however, all my basic water parameter checks have been good). The reason I suspect bacteria or virus is that my system also has an in-line 30 gallon refugium, a 55 gallon live rock tank, and 40 gallon sump. In the refugium and live rock tank some corals are growing under compact fluorescent lighting and appear unaffected, but some other species (montiporas) are dying in both the display and other tanks. I have not yet checked for heavy metals or copper. I suspect that if this was problem, the other inverts such as hermit crabs would have shown signs of stress.

System Parameters:

DISPLAY TANK (set up x 4 years)
180 gallon display tank with 120 3W CREE DIY white and royal blue LED lighting
2X Tunze Stream 6100's
1x titanium grounding probe
All monitored by Aquacontroller Pro (temp, pH, ORP)
4" sand bed
Mixture of live rock
Fish: 2 x blue tangs, 1 x sohal tang, 1 x 6 line wrasse, 1 x flame hawk, 2 x oscellaris clownfish, 1 x chevron tang
Coral: Montipora, Favia, Acropora, Blastomussa, Cyphastrea, Duncanopsammia, Pocillopora
Inverts: trochus snails, cleaner shrimp, red leg and blue leg hermits. Lots of hitchhiking brittle stars and asterina starfish

REFUGIUM (set up x 4 years)
30 gallon tank with Caulerpa prolifera
Lighting = 110 watts of CF
This tank occasionally has cyanobacteria problems probably due to low water flow and lack of snails. There are also some aocoel flat worms in this tank.
There is one scolymia and a colony of cyphastrea growing well in this refugium tank.

LIVE ROCK TANK (set up x 4 year)
55 gallon tank with about 60 lb rock. There are also a couple montipora and caulastra corals in this tank.

SUMP
40 gallon tank with 600 watts of heaters. Also being monitored by Aquacontroller.
Automatic top off system with Spectra Pure RO/DI unit
GEO Calcium reactor + GEO Kalkwasser reactor
MTC dual venturi protein skimmer
Phos-ban reactor (media changed about every 5 months)
GAC (media changed about every 4 months)
1x titanium grounding probe

Water Parameters (all monitored by Aquacontroller)

pH 8.1 - 8.4
kH 8-9
SG 35 ppt
temp: 77-79 degrees F
Ca 450
Phos: 0.04
ORP 280-320
Mg 1250 - 1300

The entire downstream portion of the system away from the display tank is plumbed to my garage, so I have very little temperature fluctuation. I do a 30 gallon water change using RO/DI every 2-3 weeks. I do not add any supplements and the fish are fed 4 blocks of mysis shrimp + cyclopez a day. In the last year or so, I had switched from Reef Chem salt to Aquavitro Salinity salt and I'm wondering if the salt may possibly be a culprit. I'm really at a loss as what to do with this system. I'm tempted to breakdown the entire system, but if the problem is a virus or endemic bacteria, I'm not sure this would help since I would not be able to retain any of my live rock, fish, or surviving corals lest the pathogen come along with the old stock. Does anyone have any suggestions as to what other factors may be causing this loss of coral?

Among the suggestions I've come up with are:
1. UV sterilizer
2. Break tank down completely and start over
3. Replace live rock and sand (possibly disrupting the pathogen)
4. Replace live rock, sand, and refugium plants
5. Do 100% water change using different salt mix
6. Some combination of all the above

But I'd like hear some other ideas

[Reef Frog]

A 100% WC all at once could be very stressful. But going back to a salt that worked for you at one time is a good idea IMO.

I would think 4 to 5 months between changes in GFO & GAC is too long in most cases as it would be completely exhausted long before that. But then again the PO4 level you listed is fine. Do you trust your test kit?

Since you suspect bacteria or viruses, a UV sterilizer could be beneficial. If you can handle the price with the knowledge it might not be the solution, it would be worth a try IMO. Personally I'd invest in it before a tank tear down.

You mention you think your flow is low. Why not get one or more broad flow circulation pumps?

Since you suspect parasites, have you considered a Bayer treatment? Never done it but might be worth the research as a possible last solution. Also, dipping a select specimen or two to see if they perk up might be a worthwhile experiment.

I tend to use using multi-promged attacks but the problem there is you never know exactly what parts of the plan actually made the difference and which had no impact. I hope you can sort it out. Good luck.

[Reef Frog]

A 100% WC all at once could be very stressful. But going back to a salt that worked for you at one time is a good idea IMO.

I would think 4 to 5 months between changes in GFO & GAC is too long in most cases as it would be completely exhausted long before that. But then again the PO4 level you listed is fine. Do you trust your test kit?

Since you suspect bacteria or viruses, a UV sterilizer could be beneficial. If you can handle the price with the knowledge it might not be the solution, it would be worth a try IMO. Personally I'd invest in it before a tank tear down.

You mention you think your flow is low. Why not get one or more broad flow circulation pumps?

Since you suspect parasites, have you considered a Bayer treatment? Never done it but might be worth the research as a possible last solution. Also, dipping a select specimen or two to see if they perk up might be a worthwhile experiment.

I tend to use multi-pronged strategies but the problem there is you never know exactly what parts of the plan actually made the difference and which had no impact. I hope you can sort it out. Good luck.

[mousefish]

I thought about the water change as well. I had intended to do a series of partial changes every two days until at least 75% of the water is changed out. Granted this only yields dilution of the original water, but it is the best and least disruptive method IMHO. I've got the two Tunze 6100's in the display tank, so I don't think flow is the issue. Any other ideas?