Starting over. You'll see lots of web advice about setting up your first tank, but here are some points that might help you if you are taking down a tank and starting over from the ground up, either in the same one or, enviably, in a larger tank. Sometimes a household move is what spurs you to start over.
I'm taking it for granted that you don't mean to "disinfect" the tank, and that you aren't doing this as a last-ditch, despairing effort at controlling algae, washing out the tank with salty brine that you let dry to a crust before rinsing, soaking heaters and thermometer, etc in a Clorox solution and simmering gravel for ten minutes in salt water.
Before you begin: You need a clear plan of what you want this new set-up to do. The new aquarium shouldn't repeat the failings of the old one; it should have new failings! This aquarium could provide a more suitable setting for the fishes you plan to keep in it, one more conducive to spawning success, perhaps, and maybe it will also be more beautiful.
This is the moment to decide whether you want to paint the outside of the back glass. Black is Takashi Amano's color. You might prefer midnight green or black-brown. Backgrounds get more airtime in the "aquascaping" page. This is also a moment to trash that inaccurate thermometer or that untrustworthy non-submersible heater. And probably to renew the fluorescent bulbs too, unless you keep a journal and know for sure how long they've been running.
Starting over might be a good moment to begin a journal, if you aren't yet keeping one.
This is also a moment to completely rethink the substrate. Will you use cat-litter laterite mixed with Flourite? Coarse sand added to your fine gravel and coarse gravel? Peat in the under layer? or organic compost? Are you really going to re-use that undergravel filter?
Assemble all the materials: Include enough clean buckets to reserve a thin scraping of matured upper layer of substrate with its nitrifying bacteria separate from your under layer of substrate, and to accommodate wood, stones and other decor, which you may want to keep wet while you work and to keep plants floating in water from the old tank. Fill a spraybottle now with clean aquarium water, or tapwater with a drop of dechlorinator.
First step: Take a wipeable grease pencil and circle the source of that slow leak! But while you have the marker in hand, circle that impossible colony of hard green spot algae, those mineral deposits that never did get eliminated the last time you set up, even an irritating scratch you want to buff out with moistened cerium oxide. Mark up the front glass like a layout editor marking a photo proof. Once you get started, none of these flaws will be apparent until you are all set up again, lights lighted, water clear, and you're settled down... and damn! there's that forgotten scratch again!
Second step: Remove the filter and set it aside just as it is, right now, before you begin stirring organic gunk into the water. This would be the worst possible moment to disassemble or clean any part of the filter. If the system is disease-free, let it run in another tank for the interim. Siphon off some clean water, not to preserve bacteria, but to preserve a founder population of the planktonic life: rotifers and copepods and the like. I have square plastic six-gallon jugs (Poland Spring Water used to come in them) for water changes and moments like this. But you'll also need some five-gallon buckets, so that the plants can be stashed in this matured water.
Remove all decor that sits on the surface of the sand. Don't let any surfaces covered with mature biofilm dry out, unless you are spot-scrubbing hair algae. That's why you have aquarium water in the spritzer.
Third step: Now carefully scrape off or siphon out ¾ of an inch of the topmost layer of the substrate into a bucket and set it aside. A square-sided plastic take-out container from the deli is ideal for this job. Don't dig too deep; all you want is the aerobic biofiltering community. You don't want to mix the hypoxic under layer with the upper layer. Rinse the gravel mixture with some clean aquarium water, if you feel you must (I wouldn't), but don't scour it or scrub it. While you work, keep this precious gravel merely covered with just enough old aquarium water barely to keep it wet. No more than that.
Mineral deposits. With the tank empty, this is the moment to remove any trace of mineral buildup anywhere on the glass or the frame. Later you'll be kicking yourself as you stare at it over the years, take it from me. I use Lime-Away and rinse meticulously afterwards. All the aquarium-product lime removers are based on acids; they all work. White vinegar is cheaper and works too, just not as fast. At the next-to-last rinse, use some bicarbonate of soda if you've used Lime-Away or any other acid to dissolve mineral deposits.
Organic residues. The other kinds of hard-to-remove deposits will likely be organic residues. McDaphnia posted at AquariaCentral:
"One thing is that calcium is not easy to remove because it is protected by layers of other stuff too, mostly organics. If some of the calcium doesn't come off, you can strip off organics with hydrogen peroxide or plain chlorine bleach. Be sure everything else cleanerwise is removed before using either H2O2 or bleach. Rinse completely before going back to the calcium remover. Calcium builds up in layers and sometimes it has to be removed the same way it formed, one layer at a time."
Soaking overnight should soften dried-out algae scum, or you could use a solution of one of the non-detergent cleaning products that are based on hydrogen peroxide combined with sodium percarbonate, like OxiClean or Oxy-Boost. Use two scoops to a gallon of warm water. Let it soak an hour or two, even overnight. These percarbonate industrial-strength cleaners are just peroxyhydrate of sodium carbonate. Hydrogen peroxide is combined with soda ash ("washing soda") in dry powder form. Activated by water, the hydrogen peroxide is released, but after six to eight hours the solution will have naturally degraded to water, oxygen and soda ash, with no chlorine or other residue. A good rinsing is in order, though. You may want to read a good 1999 article on sodium percarbonate cleansers.
Removing scratches. A useful polishing powder for buffing out shallow scratches is cerium oxide, the polishing powder used for stone-tumbling. Yes, remember "stone-tumbling?" Try the local Hobby Hovel. Some people recommend using Sof-Scrub, a mildly abrasive scouring powder. Your local auto supplies outlet might offer some further suggestions. Thorough rinsing is essential.
A brief basic description of the scratch-buffing technique formerly laid out at Mike Savad's Stained Glass Page is archived in the Wayback Machine. Melanie, posting at AquariaCentral, 29 June 2001, warned that if you let loosened mineral deposits get dry while you're working with cerium oxide, they can act as a scouring powder and put many fine scratches on the glass. She and her husband bought a special hard-packed felt cylindrical drillbit, about 3" by 3" and rented a right-angled drill to mechanize the project (they had some extensive scratching to eliminate) "After making a slurry (paste) with the cerium oxide and water, you apply it with a wet felt bit. Never let the slurry get dry," she warned; "you'll end up grinding more scratches in. The hard part was rinsing the cerium oxide out; it tended to stick to the glass and had to be scrubbed out of the silicone cracks with an old toothbrush. That only took a few minutes though, once I figured it out."
John T. Fitch and a son-in-law emptied half the water from a 150 gallon tank, taped plastic film over the water to catch slurry and used cerium oxide and musclepower to buff out scratches-- with the fish still in the tank!-- successfully. Their illustrated adventure is a FAQ at the Boston Aquarium Society's site.
Removing silicone stains. With the tank on its side, you can apply Clorox full-strength to the silicone seams, if they've been discolored by medicating dyes like malachite green or methylene blue. Use a watercolor brush or a Q-tip.
A few reminders: Don't let anything that's going back in the aquarium get dry. Treat everything from the old tank as if it were reefkeeper's live rock! Lay down a doubled-up towel to protect the glass tank from the hard surface you're washing it on; the lower corners are especially vulnerable. Don't wash anything in un-dechlorinated tapwater except the tank itself, which you'll be scrubbing out with the cheapest salt you can find. Percarbonate cleansers are okay, but use no soap, no detergent, no Toilet-Blu, etc.
Replanting. You'll never have a better moment than now to inspect each plant closely; prune off aging leaves, make divisions of overgrown clumps, and ruthlessly eliminate algal overgrowths, using the bleach technique if necessary. Clip the ends of roots. But don't steep the plants in un-dechlorinated tapwater unless you're consciously ridding them of algae; preserve the biofilm that invisibly covers every surface. It's a major source of the biodiversity of your microscopic life. So now, whether you're setting up or starting over, you're ready at last to do some aquascaping.
After you've finished replanting, then you can finally lay your surface gravel layer back again, with any additions you want to make to it, as the very last step. Then you can gently pull plants upwards, so their crowns are just level with the finished surface, before you siphon out the muddy water as I descibed for a new set-up, and begin adding de-chlorinated water.
Moving fish isn't as leisurely as the operation I've been describing. Decz described what's involved in a post at AquariaCentral, 13 Jan 2003:
"I have moved many many times with my tanks... here's what I did: First off, I moved my tanks last. I made sure all my furniture was in the new place, and then I made arrangements to move my tanks. This isn't always possible, but if you can, it will make things easier. Let me mention first not to feed your fish the day before the move! Keep that waste to a minimum! I picked up some styrofoam fish-boxes from the local outdoor store, and using my python/gravel cleaner, I filled them all up with water from the tank. The amount/size of fishboxes really depends on how many fish you have, and how big they are. It is very important not to overstock these, as the ammonia will build up quickly. Also, don't go too big; don't be buying one of those 3 foot long styro coolers because you'll snap it in half once you try to move it with water in it. Once the fish-boxes were full of water, I divided all my fish into them, trying to keep schools together. The next step in taking down my tank was going to take some time, so to keep my fish as less-stressed as possible, I placed heaters in the styro fish-boxes, as well as air stones hooked up to air pumps. Then I put the lids on as much as possible to avoid any "jumpers". I moved these out of the way so I could get on with the rest of the tank. I had an extra styro fish-box that was for my plants, my substrate and my filter media. I filled this box with water from the tank, then added those things to keep them all wet (bacteria... aka bioload). Then using camping jugs that I had around and garbage cans and buckets, I salvaged as much water as I could move. If it's a short trip, make a couple of trips if you can. Just don't move any water in the tanks, as it could cause stress fractures. If you really aren't able to move most of the water or as much as possible, for whatever reason (financial?), then don't stress it. It would be the best possible situation, but it IS possible to just use the water in the styro fish-boxes, then top up with new de-chlorinated tap water. I have done it both ways. With my 100 gallon, I actually basically did a 100% water change, because it was a long-distance move, and all my fish were fine after that. Once you've loaded up all your water, fish, deco's, substrate etc... pack up whatever equipment is left over. I always take the opportunity to clean the calcium deposits off my heaters at this point. If you aren't keeping this equipment wet, and it's equipment that runs in the water, wip them down. Dead bacteria isn't helpful in a tank and *could* cause a mini-cycle. Same goes for the tanks themselves. Now for the moving part: Here's the fun part. If you have the space to do it, leave your fish-boxes hooked up to whatever filters, heaters, air pumps you've already placed in them. This will reduce some stress. Otherwise, un-hook any filters, heaters and air pumps that you have running in the fish-boxes, and pack them up. Then tape the fish-boxes shut and move them to your vehicle. I have a tonne of freaking equipment, so it always takes a minimum of 10 loads to get it all to the truck. So, I turn my truck on, turn the heat on in the cab and place the fish in the front seat/floor area so that the heat doesn't drop. Then I do my wheel-barrow trips back and forth with everything else. Really try to avoid moving ANYTHING in the tanks. The movement can cause damage. I once cracked a 20 gallon on a move, because the heater that was sitting on the bottom of it, slid and hit the side. What a waste! Once you're loaded up, take off to the new place. Whenever I've gotten to the new place, I take the fish-boxes inside asap. I hook them all back up to the heaters, filters and air pumps and shut the lids as much as possible. Then I move on to getting the tanks inside and setting them back up. If I've ever taken more than 5 or more hours between take-down and set-up time, I have done minor minor water changes to the fish-boxes, to avoid ammonia. Anyway, set your tanks up, fill them with any tank water that you moved, (not inlcuding the fish-boxes yet), and get the heat up on them. Use warm tap water if you need. Just remember to de-chlorinate! All this moving around, and all these items, and it's possible to forget that detail (I have.. horrible!). Check your new tap water for any differences (nitrates, chloramine). You should be ready to go at this point. You've probably already moved your filters and heater and airpumps to the tanks, so leaving your fish alone in those fish-boxes isn't too great of an idea, since they've already been there a number of hours. So move them home! Use the water if you can as well! Well, I hope I haven't left anything out. And I hope this helps."