need advice on system
Hello All, this is my first ever time writing anything on this site. I am very excited, no more yahoo answers haha. I am in need of some advice, I think I have made a mistake. This tank setup was originally going to be a 75 gal overflowing into a 29 gal into a 40 gal and finally into a 10 gal containing the pump back to the 75. This plan went down the drain when drilling the 29 (turned out to be tempered, shattered.) I then decided just the 75, 40, and 10. I drilled the 75 and 40 successfuly. everything is setup. I have the 40 under the 75 containing 3 neons, 1 cory cat, and one angelfish. Been like this for almost a year when I first started fishkeeping. I know i should finish the school but ill get to that. Enough background. the problem is with the 75. It is not yet flowing into the 40 because I ordered tons of plants and stuffed it full. My plan was to wait a month for the plants to grow in, move the fish from the 40 to the 75, change the substrate on the 40, then take about 1/4 the plants from the 75 into the 40 and call it a day. I knew nothing about introducing plants which lead me to find a few snails about 3 days into the first month of plant only. I read a bit and decided to allow them to establish and just keep them in check once the tank was stocked with fish. I added one wafer to the tank once a week and i have a pretty large colony of snails now, not too much though. it has just passed a month and about 4 days ago i decided to purchase 4 oto cats as the first inhabitants to the 75. They are all doing fine, and tomorrow I planned to go purchase 3 more, until i noticed something. A worm like thing, about an inch long moving up and down in a wave like motion, yet staying still. half of it seemed to be under a rock, the exposed half sifting the ground for food. I researched and it appears to be some sort of leech, i have since searched and found one more. i thought of a dwarf puffer but realized they would be too aggressive. I looked further around the tank and saw a bug like thing dart into a cluster of hornwart. (3 days prior i notied a small green bug on the exposed top of my heater if this is any correlation) could this possibly be a damselfly nymph? I think i have a strategy to fix this system (a 6 month process so far) would it be possibly to move the 4 oto cats into the 40 with the angel, cory, and 3 neons, and then just not feed the 75 at all? would this deplete the food supply to the point where the damselfly nymph (whatever it may be) and leeches or worm things as well as snails begin to die off? if so, how long would you speculate this process would take? is there anything I could use to treat the tank to speed up the killing? without fish there wouldnt be any risk aside from plants. I would rather not remove any plants as it is a dirted tank with pretty established root systems. I figure I could just dose excel every other day and not feed anything else and eventually all the little creatures would die off so I could continue on with stocking the system. Any advice? sorry this was so long I just wanted to give all info possible. Sorry if its in the from forum, ive never used a forum before. Hopefully I will be welcomed into this planted tank community, as I have enjoyed the tank experience so far. Thanks.