A terrible secret I must admit

Haha. I'll leave the specific chem questions to someone else, but I can quickly tell you that you would be having much more success if you tripled the size of your tank. Those are some very big fish, and hard to deal with in a 100 gallon.

For cleaning the gravel, do you have any fish in there now? If not I would just drain it and start over, it seems like the water is pretty bad anyway. If stuffs goin on in there now, then I do not know what its called in the stores but there are several nifty devices that function like siphons for gravel. Stand on a chair or ladder and suck it up.

When I started with my first tanks I must have left the gravel uncleaned for months. At that point I didnt know what PH was or anything of the sort, so the deaths kind of seemed "natural." They are not though, and you do need to get that gravel cleaned.

I believe Koi get very large, and are normally kept in ponds. Both Koi and goldfish are coldwater fish as well, while the tropicals and arrowanas need warmer water. Also sounds like way too many large fish for the tank. 5 arrowanas alone would be way overdoing it IMO. As far as gravel vaccuming, yes it should be done regularly, especially considering the fish load. They sell something called a "Python" that should work well for that tank I think.

If you don't clean the gravel, nitrate levels will just about sky rocket and once you have a high nitrate level in such a large aquarium, it can be a hard task to lower them again.

As someone else said, get a python gravel vacuum system to clean the water out...you won't be sorry you bought it!

I agree with the above posts.... I don't know what kind of fish you're planning on keeping in the tank (if you don't have any already but by the sounds of things, they're pretty heavy duty which more likely than not, leave a lot of waste at the bottom...too much, seeping into the gravel....causing unhealthy fluctuations in your water chemistry. Since you say you've got all the right stuff going on for your plants yet they're still looking pretty bad, this could be the cause. Your best option is to get the "Python", it will prove most efficient on that size of tank. I have a couple 55's, a 44, and a 10 gallon and don't know what I would've done without it. It probably cuts the water maintenance down on the tank by hours.... at least in my case it does. You'll just need to be careful about the roots for the plants.

Uh... thats basically what you are doing with the python...yes.

But the python is much better, and easier to use. I'm not sure I'd use a garden hose because of all the chemicals in the plastic/rubber. :shake:

ok, I just looked at your specs and I agree, this seems ok for a 110 gallon. In using the garden hose, you can eliminame the whole thing and use a python which is specifically meant for the tank, it removes water, siphons gunk from the gravel, as well as puts the water back in the tank in a matter of minutes. I'd think in a 110 gallon you'd have everything done in a matter of an hour or less..... I suggest not using the hose method and investing int he python..... it'd clearly be the best investment for your tank yet.