Sodium percarbonate an alternative to bleach to nuke live rock?

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One comment about this particular thread's subject. If used in sufficient concentration, bleach will absolutely destroy any organic substance that would be found as a constituent of a cell wall, spore or protoplasm of a life form. In other words, it will absolutely, no-ifs-ands-or-buts destroy any and all algal cells that it's left in contact with, provided that it's sufficiently concentrated, the solution concentration isn't rapidly depleted by other organic compounds in the container, and the user leaves it in contact with the cells/spores to be destroyed for a sufficient period of time.

Since you've already settled on hydrogen peroxide, the reason that I mention this is that the same caveats hold true for its use for sterilizing items. In one sense, using sodium percarbonate has some drawbacks over using commercial bleach for your purpose. Specifically, "bleach" isn't just sodium hypochlorite. It's sodium hypochlorite and sodium hydroxide. The sodium hydroxide component does two things - it inhibits the degradation of the bleach solution under storage conditions, but it also acts to hydrolyze proteins. Hydrolysis of proteins under alkaline conditions aids in the surface removal and destruction of those proteins - this is one reason that commercial laundry detergent formulations are all quite alkaline.

But the more applicable consideration for your use is contact time and effective concentration. 3 percent hydrogen peroxide is fairly rapidly degraded to just water in contact with an excess amount of biological material. Depending on how "dirty" your live rock is, you very well may use most of the active hydrogen peroxide in the solution, and still have organic material left behind. For this reason, I'd recommend thoroughly cleaning the rock you intend to nuke, either with a pressurized garden hose or (preferably) with a scrub brush, before it's immersed in the hydrogen peroxide solution.

One other caution that you may have already thought of - hydrogen peroxide works by the organic component being oxidized, and the "leftovers" are oxygen gas and water. That's a good thing, as there's no harmful residue to be concerned about. However, and depending on the temperature of the solution and the degree of fouling on the rock, the reaction may be very violent, and given that most live rock has components that act as surfactants, the tub of rock and peroxide may foam - perhaps more than the container can hold. I'd therefore advise doing this outdoors, make the solution of peroxide in the tub, then cautiously add a piece or two of the live rock to ensure that the reaction doesn't make a mess.

@Dkeller_nc

Great info!

Just curious, for bleach what is the recommended concentration and contact time?

 

[Dkeller_nc]

@Dkeller_nc

Great info!

Just curious, for bleach what is the recommended concentration and contact time?

That depends on the purpose for which you're using it. In a laboratory, the typical concentration is 10% bleach solution, 90% water (or solution to be decontaminated). Commercial bleach is 5% sodium hypochlorite, 0.05% sodium hydroxide (the sodium hydroxide is a stabilizer). So the end result is about 0.5% sodium hypochlorite in the sterilizing solution (or cell culture media, biohazardous waste, etc...).

This concentration is more than enough to kill all microorganisms in about 10 minutes at room temperature. To be absolutely sure, I'd give the solution 30 minutes at 25 deg C.

Much like the comments about hydrogen peroxide, some of the hypochlorite ion in bleach will be consumed by reacting with organic components of whatever you put in it. If you wanted to be absolutely, no ifs ands or butts sure, you might choose to pour the bleach off after 30 minutes to an hour, replace it, and let it go for another hour. Note that 2 soaks is absolutely unnecessary to render any microorganism (or macro organism) dead as a doorknob. However, in reefkeeping, there are 2 different purposes for soaking live rock in bleach - one is to kill off undesirable organisms, the other is to oxidize organic compounds in the rock. Killing life is easy and quick, but for oxidizing remaining organic compounds, I would choose to let the first application soak for an hour or two, and let the second application go overnight.

If you choose to use bleach, a couple of comments about safety. Never, ever mix bleach with any acid, whether hydrochloric, citric or vinegar. A highly toxic gas will be the result. Always, always perform a rock soak outside, and take steps to prevent pets from having access to the tub. A small amount of bleach inside the house for (for example) doing laundry is ok, but the large quantities involved in a rock soak will generate quite a lot of chlorine gas. No big deal if you're outside, but the fumes could build up to a toxic level indoors from that amount of bleach. And I can assure you that even if the chlorine doesn't build up to the point of being directly toxic, breathing it will produce some very unpleasant effects - you'll feel like someone's scoured the inside of your sinuses with sandpaper.