DIY Sump build 55 gallon

I heard that if the tank is glass you should use glass baffles. I would definitely buy your silicone from a lfs just to make sure it is 100% reef/aquarium safe. I made the mistake a few months ago and thought I bought the right silicone when in fact I didnt and im still seeing the effects of that.. Better safe then sorry. Hope this helps

 

I've used both acrylic and glass baffles without any problem. Acrylic is easier to work with at home. You can use a saw to trim it to the size you need.

 

Acrylic will absorb some water, especially the extruded acrylic that the home improvement stores carry. It will get bigger as it absorbs water and could potentially stress the glass tank if the fit is tight to begin with. Cast acrylics may absorb less water, but I would still use glass baffles in a glass tank. The other issue you would run into is that silicone will not adhere to acrylic (very poor bond) like it does to glass. If you used silicone to hold an acrylic baffle in place, it would probably work as long as the hydraulic pressure on both sides is nearly equal. If you silicone glass baffles, they will stay put as long as the silicone isn't compromised.

For silicone, many have successfully used Momentive/GE RTV108 (semi-Clear). You can get it from industrial suppliers and online. I have purchased it at my local Grainger branch and I have also ordered it from McMaster-Carr.

 

+1 glass and U can use ge 1 silicone, NOT the type with mold inhibitor. I have used it many times on mine and others sumps/tanks and there's no issues w it as long as you let it fully cure before putting it to use, I usually wait at least a week. Aquarium silicone is pricey and usually the same thing (via RC)
Don't know what the price is on the above silicones but ge is usually 2tubes for $5. Just my .02 on silicone
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Go glass. And Be extra sure to sand the sides of your glass after you cut them and are siliconing them in. Its really easy to slice the life out of your finger running the bead. There are a few kinds of silicone you can use. Specifically the kinds that are silicone with no mildew resistant additives. Anything that states it is good to use in pottable water works too. A note on the ge1 it can often turn yellow after drying but will clear up. If it turns green or blue tinted your water has copper in it. So thats kinda neat! Ge1 works for sumps just fine. But should be avoided for sealing tanks of 90+ as it will break overtime.