I had a reverse flow under gravel filter about 30 years ago. I used a Hagen external filter filter a 302 or other not sure but it hadv inlets and 2 outlets so ideal for powering water down 2 uplifts I mean downlifts. I used baby bottle teats to secure the 12mm powerfilter pipe to the uplifts I mean downlifts or should that be downpush tubes?
Anyway that's what I did. I used Hagen interlocking filter plates with calcium plus gravel innthe bottom with coral sand on top. The 2 layers were seperate by a plastic screen called a gravel tidy. This worked for many years until I built my 130gallon system.
I recall reading an article on a study down in one of the magazines that stated dyed water only pushed through the gravel and screen within the first few inches around the tube as it entered the downpush tubes. The reasoning seem reasonable in that water will flow through the least area of resistance.
How if mine worked like that I will never know but I suspect it worked similar. Just what the other 75% of the gravel and sand accomplish is anybody's guess, perhaps denitrification.
I also doubt we will see a similar experiment carried out but it would be interesting to see done.
Anyway that's what I did. I used Hagen interlocking filter plates with calcium plus gravel innthe bottom with coral sand on top. The 2 layers were seperate by a plastic screen called a gravel tidy. This worked for many years until I built my 130gallon system.
I recall reading an article on a study down in one of the magazines that stated dyed water only pushed through the gravel and screen within the first few inches around the tube as it entered the downpush tubes. The reasoning seem reasonable in that water will flow through the least area of resistance.
How if mine worked like that I will never know but I suspect it worked similar. Just what the other 75% of the gravel and sand accomplish is anybody's guess, perhaps denitrification.
I also doubt we will see a similar experiment carried out but it would be interesting to see done.