Reworking my 90g Geo tank

[211303]

So, I just came back home from a one year study trip and found my tank is kind of a mess. Decided to rework the tank all together. Facing quite a few problems though. The tank still has 5 Geophagus tapajos, 3 cories, 20 Lemon tetra, 3 Emperor tetra, and tons of bristlenose pleco of different sizes (apparently they breed in the tank, and my parent never think they should stop them from breeding. Going to give most of them away, and remove their cave. I just don't have the place for those extra bioload).

1. Planning to change the whole substrate, as my parents never vacuum the existing sand bottom. I am afraid if I vacuum it now, the trapped gas will kill my remaining fish. Debating whether I should use 1) ADA soil capped with sand, 2) dividing the tank to area with only dirt and area with only sand or 3) sand with base fertilizer. I really want to try planting some large swords, but the Geo's sand shifting behavior is causing problem here. If I use sand+base fertilizer, I risk getting nitrate spike if the geo digs deep enough. Option 1 and 2 seems more possible, but I am not sure if Geo works with soil. Anyone have tried putting Geo in planted tanks? What substrate did you use? How thick it is?

2. Two of my Geo shows signs of internal parasite. I have Octozin at hand but I am not sure if I should treat the whole tank or just the 2 sick fish. The other fish seems healthy enough. (The dominant pair actually spawns 2 days ago, though their eggs disappear today, and I don't see any sign of mouth breeding. Guess it's typical in a community tank)

3. Going to change my filter system as well. Currently using overhead sump filter, but it's a bit noisy. Going to change to 2 Eheim 2217. Never use dual filter before though, so I am wondering how I should arrange their intake and output.

 

[mrrobxc]

I wouldn't use soil with geos. You would be asking for perpetually cloudy water. In the past, I got a bed of laterite and covered the bed about half an inch thick with netting I bought online. I then covered this netting with an inch and a half of PFS. It worked well but the betting can become dislodged over time as I moved established rooted plants around as the roots would penetrate into the laterite layer.

Also, be sure to anchor your plants in place with stones. Where the stones meet the wood is where the geos will feed since those are the areas food accumulates. You will likely have to reinforce the planting as you do water changes. In the end, geos are best in unplanted tanks but you can get away with plants if you're strategic. Be sure to leave plenty of open sandy space though.

As for intake and output, if you use two filters put both outputs near the center and put the intakes in each corner. Have the outputs cross each other. For example, after pacing the right intake in the right corner, place its output just left of center about a fifth from the center and vice versa. If you have more filters or don't like the appearance of outputs where they are easy to see, then you can put them in the corners just opposite its intake.