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Hey guys, long time no talk!
I've decided, a year after selling the shop, and 2 years after having marines in the shop, to use that lovely Aqua Medic Percula 90 tank that has been sitting empty in our living room for over 2 years...
I ordered 53kg (117lb) of indonesian liverock, shipped directly to us (it's nice having trade contacts!), however it gets shipped damp, without more than an inch of water. So I've been curing this massive amount of liverock in the Perc 90, which is roughly 70 US gal of water capacity, and my other half has done an amazing job of aquascaping, having some huge flat pieces, made lots of large and small caves
Anyhow, the usual problem is that I'm curing the rock in the tank (no fish), it's been in the tank for 10 days now, and I've put 2 doses of API Stress Zyme (1 week apart) and 2 doses of Tetra Bactazyme.
I've used Seachem Prime to try and keep the ammonia detoxed as much as possible (but is still available for the bacteria to cycle). Now today, after 10 days, 0 ammonia! However, nitrites are at 1.5ppm, so the cycle is under way, but I was shocked to see 75ppm nitrates!
There was a suprising amount of life on the rocks (less so now ), loads of crabs (40+), and a few other criters, and a fair few polyps and mushrooms, that aren't looking great now.
Got a small amount of brown alage on the rocks and sand.
Anyhow, the big question is, how much water do I change?
I've put a big dose of seachem prime to detox the nitrite and nitrate (but not enough for all the nirate!).
Do I do a 50%, or even 75%, water change before putting any animals in (after nitrates have dropped off).
I'm using 0 TDS RO water, and pleasantly suprised to find that the fairly cheap AqyaSalt from Aqua One is pretty good stuff, the PH has been rock solid at around 8.3.
So, how much should I change? (I have a spare tank and buckets to make up at least 75% of the water).
I also have spare stress zyme to put in the water after the change to boost the bacteria.
API Stress Zyme and Tetra Bactazmye suggest that animals can be added immediatly, which is clearly not true, but it's brought a 30+ day cycle down to barely 10 days, so it's not bad.

Normally I let the rock just cycle along. If you want to keep anything alive, then it's a different story I guess. Anything photosynthetic will need plenty of light, and you'll want to eliminate ammonia and nitrite. The nitrate and phosphate should be lowered as much as possible as well. Undetectable preferably, but at least well under 10ppm for nitrate and 1ppm phosphate until they naturally drop.

As for how much to change....it's pretty simple math. I generally wouldn't change more than 50% in a day, you might freak out anything alive just doing that. I certainly wouldn't suggest it with fish or inverts in the tank, but you might get away with it with the animals on the LR. I think it would take 3 x 50% or 1x75% and 1x50% water changes to get 75ppm nitrates down under 10ppm.

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Critical Fertilator: The Micromanager of Macronutrients

Thanks, yeah, I'm going to leave it until it's fully cycled and the nitrites are gone.
But I did want to try and keep as much as possible alive still. However, there isn't that much left on the rocks I guess, so it probably won't matter too much if I do a big change. I think I may just go ahead and do a 100% change, the water is made up using the same salt, from the same bucket, so I can make sure that the vat of water I'm making up will be the same temperature, PH and salinity.
I didn't have time to clean the rocks before starting to cure them, so I'll probably clean them in the syphoned water while doing the change, and give the substrate a quick clean.
At least this way there should be 0 nitrates and 0 phosphates for the tank to start with.

Where abouts are you in the UK mate? i work at Cockfields Aquarium in Manchester...

Canterbury, in Kent, my gf and I started up ReptAquarium, but we've sold it on now.

Well I'm happy to say the nitrites are dropping pretty fast, in fact, so are the nitrates! The nitrates are dropping 20ppm per day, I don't think I've ever witnessed denitrification in liverock alone, and with 53kg in a 90us gal tank, it's quite a lot!
This morning:
0ppm Ammonia (down from 1.5ppm)
0.2ppm Nitrite (down from 5ppm)
10ppm Nitrate (down from 75ppm!!)
SG: 1.0235 (yes I have a high precision hydrometer)
Looks like the only thing to worry about is phosphates now, just got to grab a test kit from the LFS, I've got a tonne of aquamedic Antiphos FE that I can chuck into the filter anyhow.
I wonder how much of the nitrate reduction is from the liverock and how much from things growning (algae etc) and from the skimmer.
I've only got the T5s on now for 3 hours a day as we had a pretty fast brown alage bloom, but most has died off now, and with appoaching 0ppm nitrate, hopefully won't come back any time soon.

Sounds like good news. That is a pretty quick drop in trates, but they are expected to drop on their own so nothing too unusual.

Sounds like you'll be ready to add new critters soon, any ideas?

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Critical Fertilator: The Micromanager of Macronutrients

Yeah I know, but having only ever used cured liverock in a tank (yes, I've cured loads of liverock before, but never really tested the water, just left it 5-6 weeks until it stopped smelling), so I'm used to putting it in a tank, adding fish and seeing nitrates going up and having to do quick water changes lol.
It's a very pleasant suprise to see 20ppm drop per day in the nitrates
Well I was going to get 60 turbo snails, probably 30 mixed hermit crabs, sand sifiting starfish, pair of cleaner and fire shrimp, a sea slug of some sort, undecided which yet.
Then of course a goby of some variety, I really liked my old yellow diamond watchman goby, so may get another, or may get a goby paired with a shirmp.
I'm not sure on the rest of the fish yet though. I'd love a copper banned butterfly fish, but I think even for a baby it would be too small quickly (roughly 3ft x 2ft x 2ft including the filter in the back).
Also undecided on corals, we've got 1 marine white and 1 marine blue 3ft T5 tubes + blue LEDs for moonlight and a 250W MH @ 14,000k.
The huge rockwork goes virtually up to the surface of the water so there is room for very bight light areas, down to large caves with hardly any light, so it's a pretty nice setup.