Recommendations for a planted tank

[alanmin4304]

It is the only heater on the tank and it is fluctuating between 23 &24 deg.

[alanmin4304]

These results make more sense: Finally caught it at the right time. There is a slight discrepency between the probe in the water for the heatpad and the probe under the sand for the thermometer but the results make more sense. The heatpad switches off at 24 deg and on at 23 deg and it dropped to 22 point something before going up to 24 again, so the water temperature is ranging from 22 point something to 24 point something. I caught the heatpad as it was switching on and the temperature under the sand, on the glass and over a heating coil rose to 33.5 deg before dropping down again. Although this is more than ideal I think I will leave it that way and see how various plants react to these conditions. It is obvious that any greater depth of sand would not be a good idea. Ludwigia repens and java fern are loving it at present but it may be a bit much for some of the swords. Time will tell.

[Warren]

Thanks Alanmin,

This is pretty much what I was expecting. With the temperature difference you're seeing it is nothing to worry about. It's less than 10'C so it will be ok.

Standard float glass will break if the temperature difference is 55'C and that's without any other stress from the water pressure. This would only occur if a certain point on the glass bottom had very good insulation and the rest was well coupled to the water ie, 50mm substrate at one end of the tank and 300mm+ at the other. In that case it's possible to get a large temperature difference that will adversely effect the tank strength. If toughened glass is used for the bottom (like my tank - Ex BNZ Bank doors) then the temperature difference can be 250'C and this is impossible to get while there's still water in the tank.

10'C will be causing a little extra stress in the glass where it joins the front, back and sides but the silicone will stretch to sort this out. The extra stress will be minor...

It is something to consider during tank design if bottom heating of the tank is going to be used and no undergravel filter will be installed. You may have to go up a few mm in glass thickness to compensate for the extra stress. Alternatively, get the bottom glass toughened.