How hot is too hot

[ChemDumb]

I've heard that a tank shouldn't get over 81 degrees or to keep it as close to 80 as possible, however, I was wondering, what, exactly, that's based on?

The reason I ask is because tonight, my little DIY nano got up to (according to Josh) 90. Mauro and Josh put a fan on it and less than thirty minutes later I was reading 85 with a glass thermometer but Josh was still reading 87.something high. not sure which is more accurate, and right now, I'm not concerned. I know what the source of the heat is, it's the MH fixture that I recently put on the tank. I'm definately going to have to keep a fan on it during these warmer summer months, however, everything in the tank looked absolutely thrilled. Granted, all I have in my tank is:

2 mexican turbos
4 peppermints
3 scarlett hermits
2 pieces of green Ric
1 BTA
some pulsing xenia
a few (dozen) assorted zoa's
a couple of leathers
a digitata ?
some montepora
and some other stuff that sue took out of her tank and put into mine for safe keeping

Yeah, it's pretty crowded in that little tank right now, but everything was extremely happy. Nothing was retracted or trying to bury itself or hiding and waiting. Everything was out and colors were all full on.

So this got me to thinking, what are the temperatures of the reefs in the wild? I looked at NOAA.org and found some data for souther atlantic and eastern gulf of mexico water temperatures for the month of Jul and it appears that the temperatures swing (over that entire region) from 76 -87 degrees for the month (the southern atlantic has the widest swing with 76-86 and the easter gulf, including the general area that the key reef is in, is at 84-87).

I couldn't find anybody that had temperature buoys at the reefs that they were taking annual steady measurements of temp (or anything else for that matter). So I guess that my question is, why should I expect that 86 degrees is bad for my tank? I understand that drastic changes are bad (that goes without saying), but if the temperature itself gets to that point in the summers in tropical waters, what's all the fuss?

Lou

 

[maurod]

BTW, Lou's tank hit 88 last night (I never saw 90). Nothing died.
Lou's tank would be light 4 peppermints if Scavo would ever pick them up.

M.

 

[randoma]

The time that our tank overheated (don't know the exact temperature but assume it was 86-90 or so), everything looked fine that day. Everything looked fine the next day. The 3rd day, several pieces of hard coral RTN'd basically overnight. Additional pieces RTN'd over the next week. As far as I can tell all the soft coral and inverts (no fish in the tank) were fine.

 

[Salty Dog]

Our tank hit 92 the other day - all the livestock is fine, as well as the inverts - I think we lost a few hermits, though. Coral is still a waiting game.

Eric

 

[MarkO]

Based on my experience, my corals will start to wilt around 89-90 deg, at 91ish-92 things start to die.
I think the problem is the O2 content which depletes exponentially as temperature rises.

 

[this is me]

you don't see the effect until at least a couple weeks later.

 

[maurod]

you don't see the effect until at least a couple weeks later.

A couple of weeks? I cant believe a single or two day heat spike causes mass death weeks after the event (a few days later, perhaps, due to chemistry changes or unseen death...). I would believe that another event or mistake would be the cause of the mass death weeks later.

M.

 

[MikeG]

A couple of weeks? I cant believe a single or two day heat spike causes mass death weeks after the event (a few days later, perhaps, due to chemistry changes or unseen death...). I would believe that another event or mistake would be the cause of the mass death weeks later.

M.

I have seen the same thing where some things will die in a couple days but you continie to lose things to RTN over weeks or even months. There definately could be other things going on but they were not apparent.

 

[ChemDumb]

ok, I can understand the whole lower oxygen thing as potentially being a really bad thing, however, I have a tone of flow for the size that the tank is. There is a lot of surface area that is moved regularly. I could understand that things would die for lack of oxygen, I just wish there were a simple test of O2 available.

My greater question, however, is, what other changes occur, other than oxygen, when the water temp rises? I understand that there have to be temperature limits that the corals can withstand, what I don't understand is why they can handle the higher temps (and subsequently cooler temps) in the wild but not in our reef tanks? Are there any other changes that are KNOWN that occur in the tanks when the temperature rises? I also understand that the large temperature swings are bad due to the amount of stress that it incurs on the tank. Is it possible that the reason for these tanks having problems from over heating is more likely due to large daily swings?

Just somethings I've been thinking about.

Lou

 

[smcnally]

I think this is entirely dependent on so many variables that it is silly to tell people that their corals will die off in a couple weeks. It not only depends on how hot the tank got, but how quickly. It also depends on how long it took for the tank to cool down and what the parameters were at while all this was happening.

 

[Jim Tansey]

I often read comments like this and think is this an opinion or is there some factual informational behind it, unless some additional info is provided I usually place it in the circular file.

Jim

 

[ChemDumb]

I guess that's really what I'm asking. Is there any real data on the changes that occur in a tank or in a reef during these temperature spikes?

 

[LockeOak]

Mortality of corals from temperature stress is affected by the temperature severity, duration of exposure and simultaneous light exposure. It's important to remember that coral bleaching/death can be a result of stress to the photosynthetic algae in the coral, the coral animal itself or both. The symbiotic zooxanthellae are more easily photoinhibited by high light exposure when temperatures are high, that is, they get "overloaded" with light and begin creating free radicals of oxygen that can damage the photosynthetic pathways, sometimes permanently. (If you're curious, this is partially due to the fact that cells try to cope with too much light by channelling excess photons to xanthophyll pigments that heat up to shed the extra energy, which in temperature spikes only makes the situation worse). I'll copy-n-paste a couple of paragraphs from a relevant paper:

"Laboratory studies have confirmed that symbiotic dinoflagellates are usually less heat tolerant than their host, and that different symbiotic associations show different levels of stress tolerance (Clark and Jensen 1982, Jokiel and Coles 1990, Iglesias-Prieto et al. 1992, Fitt et al. 1993, Fitt and Warner 1995, Warner et al. 1996, Iglesias-Prieto and Trench 1997). Indeed, when one of the most sensitive biochemical assays of heat stress, namely heat shock protein (hsp) production, is measured in corals exposed to a series of elevated temperatures, hsp production in the coral host is not elicited until after a 2 hour heat shock at 33' C [91.4'F], whereas significant algal loss has already taken place within a 2 hour exposure at a lower temperature of 30' C [86'F] (Sharp et al. 1997). Such a result is supportive of the view that the algae are more susceptible to thermal stress than their hosts. While shedding of host [animal] cells containing symbiotic algae may not be prevalent in the field at current sea surface temperature, experimental laboratory protocols involving rapid and large changes in temperature may in fact induce this type of bleaching (eg. Steen and Muscatine 1987; Gates et al. 1992). It is possible that localized hydrographic conditions may exist on a reef that would involve animal stress in a fashion that would include release of animal cells containing symbiotic algae; however, it seems unlikely that such a mechanism would act on regional or even reefal scales." Fitt WK et al. 2001, Coral Reefs.

So, basically, I read this to mean that it's the algae that die off first; it's pretty difficult to kill the coral animal outright with a temperature spike (though aquarists manage some difficult things sometimes!). This die-off is exacerbated by high light levels, so if you come home to a hot tank, turn your lights off immediately. How susceptible a particular coral is depends on how light-adapted it is, what kind of symbionts it has, etc. The paper quote is by one of my Ph.D advisors.

 

[LockeOak]

I should note that my personal experience it that I've come home to a tank at 87.5 degrees under power compact lighting (albeit with SPS only about 5" from 130W of PC lighting) and after bringing the temp down to 81-82 over the course of an hour or two I didn't lose anything, including zoanthids, mushrooms, acropora, montipora. This was a couple of months ago. If I had had metal halides over that tank at the same temperature perhaps it would have been different.

 

[ChemDumb]

interesting, so people are doing research in the area. I'll have to look more into it.

Lou

 

[csb]

I try to keep temperature swings within 4 degrees per 24 hour period. ... so if the tank gets hot, try not to panic and immediately correct the temperature... the abrupt temperature change can be worse than the high temperature itself.

Always have fans blowing your tank ... it's better for temp stability and gas exchange at the water's surface.