Whats a safe short term drop in pH for SPS

[UK_Pete]

Whats a considered a safe level for pH to drop to short term in an SPS tank? IE if something dies and it causes the pCO2 to rise to say 2000 ppm, I found a graph that seems to show the pH will drop to about 7.45

http://publishing.cdlib.org/ucpressebooks/data/13030/6r/kt167nb66r/figures/kt167nb66r_fig040.gif

If I am interpreting it correctly. Would this be safe for a day in an SPS tank or is that likely to trigger RTN or some other distress, and if 7.45 is considered dangerous even for a day, whats considered safe? Could the pH go even lower that this for a day or two?

Thanks, Pete

 

[Keithcorals]

I've seen things lose color overnight when my ph dropped to 7.5 so I would say for sure that wouldn't be a safe ph even for a day. But unless you have a ph probe you wouldn't have a good way to know the ph was that low after the fact. I think anything under 7.7 is not a good idea

 

[Frozn]

I would say any minimal swing is safe. Within a few points should be fine. However it is the big changes in salinity, temp, ph etc that causes the most stress. 7.5 no matter how stable sounds too low in my experience

 

[Randy Holmes-Farley Verified Community Expert]

At pH in the mid 7's, aragonite skeletons can begin to very slowly dissolve. How long you are there will determine how bad that is, but I wouldn't want to keep an aquarium at less than about pH 7.7-7.8.

 

[UK_Pete]

This is only as a worst case scenario, IE I am away from home, a large fish dies, and its digested over a day so puts 15 g CO2 into the tank, and it takes the tank a day or so to get rid of the CO2. pH would I think drop to about 7.5 - with SPS in the tank, would you guys expect that to result in a snowball of die off? I can handle a bit of short term bleaching etc, but really I mean death of corals / triggering RTN etc.

 

[Randy Holmes-Farley Verified Community Expert]

An even worse case might be a power failure, where the tank cannot effectively release CO2 to the air.

 

[s2nhle]

I had my tank with PH around 7.7 or 7.8 for awhile and the color of my SPS is faded out. I trimed my Chaeto down a little bit and add refilled my Kalk. My ph is stable above 8.1 and I can see the polyps of my SPS is bigger and the color is starting to come back.

 

[UK_Pete]

Yes I actually did suffer a 2 day blackout once, although I was at home. So borrowed a generator and ran it for the 2 days. I fed it back into my house mains but obviously it was not clean enough power and a couple of things stopped working after that, I can't remember what but I thought 'won't do that again!'. But it ran the pumps and a couple of airstones. So since that I have got a UPS and for the next long trip away, it will be rigged up to a couple of 6w circulation pumps and maybe 10 watts worth of airstones - whatever I decide is the bare minimum, and thats partly what I'm trying to work out now. The less I power from it the longer it will run for. No need for lights, but oxygen / CO2 / circulation are the number one priorities I think. Maybe the peristaltic if I do dose NaOH as this would help counter some of the CO2 (most useful in the die off situation).

So if I had a 50g fish die (10g protein), that would produce 15g CO2 as its metabolised by bacteria if I understand correctly. If that happens over 1 day, with 500 lph air going into the tank from outdoors, and 2.4 litres of kalk going in a day (or equivilent NaOH), it would average about 1450ppm CO2 for the day. Which looks like it would produce a pH of around 7.6 from that graph I linked to, but whether this would result in a snowball tank crash i don't know.

BTW the 2.4 litres of kalk a day comes from another calculation to prevent pH going too high with only 500 lph air going into the tank. Although more kalk would keep the pH higher in the case of die off, it risks pH going too high under normal conditions.

 

[UK_Pete]

s2nhle thats interesting thanks. If 7.7 for a while is OK, and only a bit of fading happened, it wouldn’t seem too risky to allow 7.6 or perhaps even 7.5 for a day, but I would prefer to hear from someone who actually had experienced that rather than make that guess myself!