Thanks Dawn! I appreciate the compliment and great suggestion. You got me thinking. Taking a week between steps would definitely make the project feel less daunting. On the other hand, I may want to stick with it and just get it done. I suspect I'll do something in between. I do appreciate your 2 cents!
I agree, the rocks are probably not operating at peak efficiency right now, bio-filtrationwise. However, I have a very low bio-load and a gargantuan filtration capacity in the plants and (undisturbed part of) the sand bed. I suspect that my ten pounds of live rock (in a 180 gallon tank) are a rather small percentage of my total filtration capacity.
I'm most concerned with the sand bed disturbance and Hydrogen Sulfide. Here's a good article by Randy Holmes-Farley:
http://reefkeeping.com/issues/2005-12/rhf/index.php
Mr. Holmes-Farley seems like a very smart guy. The way he rattles off chemistry equations so conversationally blows my mind! I was always good at math, but chemistry is a challenge. It's important to remember that he's addressing reef tanks, which are significantly different to what I have, which is essentially a 180 gallon refugium, with no reef to filter and very few fish.
He addressed what I'm doing in my upcoming project almost exactly in the article here:
"8. If an anoxic sand bed needs to be removed from a reef aquarium, and there are organisms that cannot be relocated out of harms way, the following precautions may be useful based on the principles detailed in previous sections, although I've not tested any to see how effective they are:
A. Remove delicate organisms from the tank system, if possible.
B. Perform the change when the lights are as bright as possible, preferably near the end of the light cycle. The lights drive the O2 concentration higher, speeding the oxidative removal of hydrogen sulfide, and the light itself will catalyze the oxidation of H2S.
C. Maximize aeration. A high oxygen level drives hydrogen sulfide oxidation, and high aeration will drive some off as volatile H2S gas.
D. Add an iron supplement to help catalyze oxidation of hydrogen sulfide and the precipitation of ferrous and/or ferric sulfide. Use one chelated to an organic; either ferrous or ferric iron will work.
E. Pass the water over iron oxide/hydroxide (GFO) to convert hydrogen sulfide to elemental sulfur.
F. Pass the water over activated carbon, which may bind some sulfide, and may also catalyze the oxidation. If forced to choose between carbon and GFO, I'd pick the GFO media."
Points B, C and D are especially helpful and doable for me. I already have high oxygen levels, indicated by my grasses producing oxygen bubbles later in the day. I also have a large bottle of Iron supplement ready to go.
After taking a quick look, I'd estimate I'll be removing/disturbing around 10-20% of the sand. Luckily, I have no sensitive organisms, like corals. Hopefully, between the rest of the sand bed and the plants, the tank will be able to weather the storm.
