Good luck on your tank. Have you boiled your rocks? Soap or any kind of cleanser is a big no-no. Sandstone will absorb stuff, so I would stick to vinegar as a cleaning agent.

Chlorine will dissipate out of the water within 24 hours so you don't need any chemicals to start. Don't start with plecos. Buy cheap hardy fish [swords, danos] until the tank cycles. I don't like slate it has sharp edges and sometimes comes apart in shards. Let the tank run for a few days before adding fish. Check for leaks in tank and filter. Most tanks go through a cloudy water period before a natural balance is achieved. Good luck, it's a great hobby.

I was just doing resesarch on rocks. (my two semesters of geolodgy long ago didn't help, sigh) Here goes. (I'll sign off now, rather long, best Sherry)

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Before I mention rocks, your fish list is mixed. Ie your combinations (I am assuming you might mean all together) require different environments mates. cichlids need higher ph, hardness. Danios which type, but giant dianos (again much research as I was considering them NOT now... except for large globe tank where they can go round and round, they need huge tank with a big enough school or can be agressive)..

Schooling fish, tetras, dianos so on, can be very agressive, the school reduces this agression. Watch them carefully at the store, you will spot this behavior... bigger school bigger space (certainly 55 is big enough for most save for giant diano)

Gouramis, again get agressive - some exceptions, but as they mature they set up territories like bettas, and the weakest gets picked on and disease sets in.. then the next one, so on... (just gave them away except for one for each tank, and one even went after my catfish) these were dwarf, unless you have a huge long tank several feet of territory each, pleanty of wood plants. And then their is the dreaded gourami disease, which from vet research may even be viral due to their being bred in horrific conditions now. Even called ticking time bombs by breeders. There are always exceptions. I love this fish, but was very dissapointed and after researching seems a common problem these days.

Most of the fish you have listed are not of the peaceful nature, certainly not the gouramies and esp the cichlids! lol

I personally do not use fish as water cyclers, cycling can be done and fish need not be stressed. Just go slow and add two to start so on.

Some dianos are so frenzied for other fish, slower moving ones, they discombobulate the whole tank... (again from reading much of others experience) (sorry for my horrible spelling)

So, decide on cichlids which would be alone and possibly with loaches depending on type. (loaches are a great fish mho)

Here is a link mentioning plecos with cichlids.. some do some get eaten (plecos that is)

http://cichlidforums.com/showthread.php?threadid=115

Loaches (some have spines so have to be careful when bagging) are a schooling fish....

Loaches and cichlids?

http://www.aquariacentral.com/forums/showthread.php?t=27255
(where paste is from)

Go to www.cichlidscene.com

This website shows you that you can mix clown loaches with Midas, Red Devil, and etc.>

http://www.cichlidscene.com/

Plecos get huge, and need wood. (ie don't overstock, even 55 will fill up fast with fish that need territory, and plecos do as well, under logs mostly, I had two and each had his place, then one day the one was dead (think he sat on heater and I didn't realize he wouldn't know to move, oops)

Mollies need higher salt content then the other fish you've mentioned. Mollies would go with platies, guppies which also like higher salt. Mollies would be nice food for most cichlids.....

Rocks:

Question number one is what type of environment for which fish are you using rocks. This will make a difference if the rock is safe or not. Cichilids can handle rocks that contain calcium/lime so on (sorry did much research but was focusing on something I found, granite/sheitz (sp) rock. so read links to your specifics)

(after many hours, I gave up and am going to take it to my college alumni geology department)....(found it when a hole was dug up in nyc, but has mica and iron in it so not sure if its safe except for my blind cave fish which was not what I was going to put in this tank but may change cause it looks great)

First, ones collected from rivers, lakes, so on with fish safest.

Vineger not best test (read in link below). Sandstone can contain lime. Many many types of sandstone so depends. Best test mho is if fish living in water with rocks in it.

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I agree, bleach and other cleaners not good choice, may be softer part of rock that absorbs. You can use hydrogen peroxide instead. I use it to clean all things as it breaks down into water.

http://www.skepticalaquarist.com/docs/aquascaping/rocks.shtm

Has great photos, and can be beginning to further research.

http://www.fishforums.net/index.php?showtopic=55806

http://www.thekrib.com/TankHardware/rocks.html

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Pillow Lava: (I grew up in Oregon and collected obsidian but never heard of this type) Make sure no glassy sharp edges otherwise safe.. IE inert.

http://en.wikipedia.org/wiki/Pillow_lava

Pillow lava
Pillow lava (NOAA)Pillow lava is the rock type typically formed when lava emerges from an underwater volcanic vent or a lava flow enters the ocean. The viscous lava gains a solid crust immediately upon contact with the water, and this crust cracks and oozes additional large blobs or "pillows" as more lava emerges from the advancing flow. Since the majority of Earth's surface is covered by water, and most volcanoes are situated near or under it, pillow lava is very common. Examples of this can be seen at Llanddwyn Island.

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Sandstone: Well, as you can see in the following link, there are many types. IF you got it from river with fish (fresh I assume) then it would be ok. Again, it is the one worth questioning, as there are many types. I put my baby guppies in my 20 long with rock, both to cycle (I always use bio bugs, bio filter from other tanks, and change water often, and add fish so slow, never get spikes so on) But want to see about the rock, so far all is well)

Pillow Lava: (I grew up in Oregon and collected obsidian but never heard of this type) Make sure no glassy sharp edges otherwise safe.. IE inert. PS. Wikipedia is great as one link leads to another, can go on forever! So, some sandstones safe for certain fish, some not. Again, depends on fish/rock combo.

http://en.wikipedia.org/wiki/Sandstone

Terrestrial environments
Rivers (levees, point bars, channel sands)
Alluvial fans
Glacial outwash
Lakes
Deserts (sand dunes and ergs)
Marine environments
Deltas
Beach and shoreface sands
Tidal deltas, flats
Offshore bars and sand waves
Storm deposits (tempestites)
Turbidites (submarine channels and fans)

[edit] Types of sandstone
Sandstone with quartzOnce the geological characteristics of a sandstone have been established, it can then be assigned to one of three broad groups:

arkosic sandstones, which have a high (>25%) feldspar content and a composition similar to granite.
quartzose sandstones (also known as 'beach sand') which have a high (>90%) quartz content. Sometimes these sandstones are termed "orthoquartzites", e.g., the Tuscarora Quartzite of the Ridge-and-valley Appalachians.
argillaceous sandstones, such as greywacke, which have a significant clay or silt content.

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Question -
Can I use rock from a creek to decorate my fish tank? If so, what do I do to clean the rocks? Thanks very much!

Answer -
Dear Jay,
Sure. Most all rocks are "aquarium safe" in a sense. But some do in fact release mineral substances that can raise your pH and hardness to levels that your fish may certainly not appreciate.

Try is setting the rock in a small bucket of water, testing the pH before adding the rocks and then again about a week later, if the pH has risen then you know those rocks may not be safe. Calcarous rocks are good for african cichlid aquariums whom love harder water.

~The way I clean rocks is to thoroughly scrub the rocks in hot water. Don't use any soaps or chemicals. Just a very good scrubbing with hot water under the tap.

I really hope this helps!
Only my very best wishes!
Karen~
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WEll, not applicable but beautiful photos of rocks! As I said, I searched everywhere! lol

http://www.terragalleria.com/pictures-subjects/granite/granite.all.html

Hi
Sounds like you're getting good advice but here's my two cents anyway lol
Last March I setup a 150 using painted, expanding foam.
The only natural materials are the plants and fish.lol
The advantages of this material are that it can be shaped ,colored into anything your imagination can think of.
It is stable ,light weight and costs almost nothing compared to real rock. I needed to cover the entire back of the tank after doing a repair on a cracked glass and it's set into a wall so only 3 sides are viewable anyway.
I first used this "Stuff" for a waterfall in a paludarium,then a "rift lake" setup and for a backgroung for a reef setup. It has worked well in all these setups
I don't think I'd ever go back to using "natural" materials again.lol
I first learned about it on the "Dutch Vivaria" sites and have been experimenting ever since. If interested I could point out some methods for this entirely different approach to "decoration"
Good luck with your new tank!!! gary