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Walstad low-tech 40 B, central FL biotope, creator of Jordanella floridae x Mobula birostris hybrid
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Discussion Starter · #1 · (Edited)
Hi all,

(Photos at bottom of post)

I'm setting up a new 10g tank for a Florida blue crayfish (P. alleni). It will be an unheated, unfiltered, low-tech, natural planted Walstad setup. I built a large foam/Drylok background for it covering the entire back and about half of the bottom, including hiding caves and a midwater "planter" area. (Weird setup, but it's an experiment...)

Somehow, though, the background bent during construction, such that the 90 degree angle between the back and bottom pieces is more like 92 degrees now. Therefore, it no longer sits tightly against the back and bottom of the tank, but has about a 1/4 inch gap along the rear bottom edge.

I was planning on using just a couple of spots of silicone to hold it in place, to facilitate future removal and reuse. But due to the warp, for it to be held tightly against the bottom and rear glass, I'll have to use a lot of silicone, and destroy it to remove it later.

Also, unless I seal all the edges, the edges will have very small gaps allowing water through.

QUESTION 1: Will leaving this gap behind the background be likely to endanger the tank, due to stagnant or anaerobic water behind my hardscape?

The bottom of the tank will be covered in about a half inch of MTS (only towards the front glass) under about half an inch of medium sand, and will have Ludwigia repens planted in it. The sand will extend up into the bottom of the caves. The plant tray above will have about 3/4 inches of MTS and 1/2 inch medium sand, and will hold as yet undetermined plants. It will have floating hornwort and Salvinia minima as well.

Animals include the single crayfish for sure, and maybe a 3-inch tadpole madtom (haven't decided yet... I think he's been occasionally eating small tankmates in my 40B NPT, but I'm concerned for the crayfish's safety, especially when he molts). I may also add a few small top-dwelling fish, such as mosquitofish (Gambusia) and/or golden topminnows (F. chrysotus), and a few grass shrimp.

(And yes, I know people say crayfish quickly destroy NPTs, but even with two crayfish in the tub, the plants have only multiplied).

QUESTION 2: Any advice on keeping a tadpole madtom with a Florida crayfish?

Thanks for any advice!

The completed background. It's made of carved styrofoam sheet and spray foam, covered in Drylok dyed with cheap acrylic craft paint.

The light bulb is just to provide a sense of scale for the "planter" feature.

Due to the warp that occurred during construction, the bottom corner no longer fits tightly against the glass unless the background is forced into place.

Most of the carving has been done, but no Drylok has been applied. The white styrofoam was held together with round toothpicks, most of which were removed after the spray foam was applied and "glued" the pieces together.
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