remove the substrates.. When consumed coconut/walnut sand woodchips etc etc have sharp edges and when consumed tear and damage the intestinal walls. That plus you are looking at a much greater possibility that your iguana can consume it die from constipation. Seen that many times. I'd suggest simple things like newspaper, linoleum stick on tile things like that.. You'll save time and money and there's far less risk.
As for your iguana... 55G tanks are horrible and add to your iguanas problem.. Which is basically a very defensive reaction NOT aggressive from the way you word it.. This is normal. When you use tanks you only aid in the iguana's reaction to you because you are approaching it from the top.. In the iguana's eye its instinct tell it that you are a swooping down to eat it. Keep in mind that Iguanas are NOT domesticated animals like cat and dog.. Their natural instinct has not diluted down so the will get quite defensive. You will want to look at a front opening cage preferably all sides being plywood except for the front. You can buy already cut wood at most stores (or they can cut it for you, typically for free).. A 4ft wide x 2ft deep x 4ft tall would be ideal for an iguana that age.. You would be looking at doubling that dimension for an adult iguana.
Anyways for your iguana.. You want to pull him out as quickly as possible. It may/may not puff up at you. If it does that is a sign they are trying to make themselves look bigger.. they will try to run and hide and when cornered (or sometimes they hold their ground) - The bending of the body and flicking the tail is a normal defensive reaction. A bite is typically the last resort but if you are continuously scaring the hell out of it, I can see it turning from defensive to aggressive and go for the bite first.
First thing.. Stop it from being able to do this. The open-front cage will start to help. Other methods are to toss a hand towel over it. This is going to freeze most iguanas in their tracks.. Almost always in fact. It confuses them and helps you so it cannon scratch the living hell out of you. Next just simply retrieve the little bugger from the cage and work with it. Taming iguanas is a matter of time and patience.. You want to hold the iguana as many times a day as possible and place it back in.. Direct interaction however is not always the way to do.. They will just close their eyes and block you out. Instead since you seemingly are a bit behind with its age.. Try to go in a room that is fully closed off, small and NO escape routes, places to climb and hide break furniture etc. Bathrooms can work great for this. I would simply set it down and play on tablet, read a book whatever and let it go on the floor and eventually its going to start moving around. As you go through this more and more offer some fruit, flowers or other favorite foods. Just leave it be while you do this, no sudden/fast moves towards you. The idea is to let your iguana tolerate you - when it starts to it will eventually crawl on you and you can start to interact with it, hand feed some food etc. Just keep doing this it can be days, weeks.. Even months. The first goal is to let the iguana tolerate you and to get it to be nice and workable never happens for some people.. For others they find their iguanas dog tame from the start or they find they get the iguana somewhat tame after a few months then it can even take a few years before they fully mellow out. As they get bigger they are seemingly more interactive with people (for better or for worse). All a flip of a dime really as far as that goes.
1 or 2 other points of interest. fishy tanks and heat spectrum = nearly impossible. Basking temps should be in mid 90's during daytime opposite end of the cage between high 70s to mid 80.. If you get your basking zone at 95 mid end at 85 and your cooler zone in mid to high 70's then your golden. Thats impossible to do in a glass tank as heat will all rise and as far as iguanas go, they are climbers and seek comfort in the height of the cage.. They will not always go to the lower end of the cage but they will quickly establish their territorial boundry within their cage so upper/lower end of cage helps that factor.. In a fish tank they do not have this sense of security.
And do NOT back down from the iguana if it tries to whip you or flashes it teeth. At 7-8 mos is might hurt a little to take a bite, it can draw some blood and the tail can sting.. but they recognize people withdrawing from the cage if people leave them alone with those actions and they will only continue to do so. A 7 or 8 mo old iguana will not do nearly as much damage as an iguana that is 3-6 foot long.. I've taken a few bites in my time. I have a couple of battle scars, a few bone fractures from sheer jaw strength.. Nannette who responded even had to do a surgery to repair a ligament in one of her fingers.. So now is he time to work on your ig. One time a day holding it is simply not enough.