drobbyb
Bowhead
Leave them in for the water change.
Although I still feel, jmain, that the presence of ammonia in your tap water and the large number of fish (creating a lot of ammonia therefor) and the large size of the tank (necessitating an enormous amount of work for the water changes) have created a very, very difficult situation (one of the strongest needs for having the fish re-homed that I've ever seen,) its still going to be imperative that water changes be done to at least bring the nitrite down and the ammonia down to the level that's coming in from the tap water. That level will still be better for the fish than a higher level if they are left to choke in their own circulating waste. Unfortunately, the growing of biofilters is a slow, slow thing and all of our attempts to speed it up usually don't help that much in actual practice. Marine mature media will not carry the same species of bacteria unfortunatly, so you'll need to seek mature media from a freshwater filter (perhaps that's what you were planning.)
~~waterdrop~~
OK, not sure what you're thinking when you talk about aging the water. Thinking that "aged" water was good was an old tropical fish hobby thing that went out the window decades ago. One aspect of it was that back then all the water authorities used chlorine in the tap water and you could let it gas out by sitting it and never have to use conditioner. Nowadays most authorities use chloramines, so that the effect will last longer out of the pipe and sitting the water will do nothing to clear the chloramines from it. That needs to be done with a conditioner and on top of that most modern conditioners to extra things beyond just removing chlorine compounds. A top choice for beginners is Prime, which is quite concentrated and quite good at converting ammonia into harmless ammonium (use of this would of course be a good thing for you at water change time.)
I believe the other lore about aged water perhaps had to do with old tank syndrome but I forget the story for the mo so maybe OM will come along and remember it. There was a thread on here somewhere that did a fabulous job with some of why aged water had been so highly thought of prior to people having more access to practical water chemistry for tanks.
Ammonia won't go away from water just sitting around unfortunately.
~~waterdrop~~
2) Put in a ton of plants to cleanse the water of ammonia and save your fish.
In practice though its a tough road for a beginner. First of all, I believe (if I'm remembering right.. beginning to forget,lol, cause I'm a distracted guy!) you've got a big array of big fish in there. By contrast, what planted tank folks do is put in a small number of small bodied fish to provide just a trace of ammonia, depending on tank size (the big 75g is in your favor here!)
So we're really, technically, right back to where we were to begin with, which is that the reason most beginners like (even if they don't know it yet, lol) a good biofilter and a fishless cycle, is that production of ammonia and nitrite is *fast* and biofilters are *fast* and unfortunately these other ideas, while good in their own way, are just slower by comparison!
~~waterdrop~~
I ended up getting some seasoned gravel from the place that I do volunteer work at to help with my bacteria colony in my tank (well that is the plan.) Also I took 3 gallons of clean water from there and added it to my tank. With me going over there once a week right now I'm just going to be bringing a 5 gallon bucket and transporting 5 gallons at a time that is needed.
I ended up getting some seasoned gravel from the place that I do volunteer work at to help with my bacteria colony in my tank (well that is the plan.) Also I took 3 gallons of clean water from there and added it to my tank. With me going over there once a week right now I'm just going to be bringing a 5 gallon bucket and transporting 5 gallons at a time that is needed.
As afishdude said, there is not bacteria in the water. Technically there might be a little bit but there are thousands and millions of times more bacteria on the surfaces in the tank (which is primarily the filter media).
A chunk of filter media will do far more for you than anything else you can get out of the tank, including the water or the gravel... while they both will have bacteria, the amount will pale in comparison to the amount of bacteria in the filter media. Most of it is in there. Gravel is better than the water since it's a surface where the bacteria will multiply.. but still not nearly as good as the filter media.
Low light fast growing plants that can get their CO2 from the air above the water are the best choice for helping control ammonia in a new tank. The typical recommendation is things like duckweed or frogbit. Another ammonia sponge is water lettuce. You will want to cover most of the water surface with floating plants to get the maximum use of the plants to remove ammonia.
Did you put the gravel into the filter where it is getting a good water flow? If not, you, may want to do that to get the most that you can from that gravel sample. Any simple bag can hold the gravel where it is needed without the gravel going places that you don't want it in the filter. I see more and more statements like Chrissi's these days about how little bacteria there are in the gravel, but I used to see estimates as high as 30% of the bacteria being in the gravel. I really don't know which is right but either way you need your cloning material in a good flow path and by preference in the filter.