I had the InTank chambers for chamber 1 and 2 but ultimately I took out the InTank in the 2nd chamber because my 3rd chamber was dropping too low. I do have my 1.0 dropped about 3 notches down.
I have the InTank Chamber One (FL12MR) and InTank Chamber Two (FL13MR) setup for the Fluval EVO 52L (Fluval EVO 13.5). Chamber One comes with a Water Director (weir) and false wall plug (for "plugging" the chamber two hole). I also have the supplied Fluval Return Pump that is rated at 500 lph and the additional Fluval M50 Heater (A781). I have a black tape "triangle" showing my main aquarium at 1.5cm ( 9/16") from the top to show the operating ON height and to allow for evaporation and to mark the level for the addition of RO/DI water to return the tank to a 35 ppm salinity.
The variation in height of the three chambers is often a concern, and whilst there is some variation in height between the OFF condition where the three chambers and the main aquarium are all at the same height compared to the ON condition, it's not so great - if you measure it and understand two "failure" conditions.
I have "mechanical" floss media in Chamber One @ Level 1: 3.5cm (1 3/8") with 500ml Seechem Matrix (in a bag) @ levels 2 & 3 (divider removed).
I have "bio" media in Chamber Two @ level 2: 250ml Seechem De Nitrate (in a bag).
I also have Red Sea Activated Carbon (in a bag) which I could add/remove from Chamber Two @ Level 3. I don't use the Activated Carbon at the moment.
The Fluval Pump delivers the quoted flow of 500 lph and I measured it with a jug. The flow rate doesn't vary with/without media in the chambers - that's because the chambers are open to the atmosphere and the pump simply pushes water out (it would be different if the levels changed dramatically or the pump was starved of water to pump).
The OFF condition has all levels at 2cm (13/16") from the top. I don't have this marked as I'm only interested in the ON condition when the water level rises in the main aquarium to 1.5cm (9/16") from the top of the tank.
The media causes the ON condition levels to vary, but not as much as some users have reported. The reference level is 2cm (13/16") and the measured levels are chamber one: 2.4cm (15/16"), chamber two: 3.4cm (1 5/16") and chamber three: 3.6cm (1 7/16"). So the maximum drop on any of the three chambers is 1.6cm (5/8") and the increase in the main aquarium is 0.5cm (3/16").
So the first thing to note, if there is an interuption to power, the levels will revert to the OFF condition and the levels in the chambers will rise and the level in the main aquarium will drop - neither reach levels that are anything to worry about.
The InTank Chamber One comes with a Water Director (weir) that is 3.8cm (1 1/2") below the top of the aquarium.
The second thing to note is that with the plug in chamber two, the levels in the three chambers will be seriously "upset" if the main aquarium height decreases (through evaporation) by 2.3cm (7/8"), the levels will start dropping and chamber three could start to empty, when water can no longer flow into chamber one. That's 3.4 litres of water that needs to be lost from the system through evaporation. That's also one heck of an increase in the salinity of the tank water as well!
I put floss in chamber one @ level 1 - so it is easy to inspect and remove it as it gets dirty. I didn't put any floss in chamber two @ level 3 - it isn't so easy to inspect or remove it as it gets dirty.
I put Seechem Matrix in chamber one @ levels 2 & 3 where the flow rate is 500 lph. That's a flow rate that is much more than the recommended flow rate of up to (a limit, not a target) for Seechem De Nitrate of 200 lph.
I put Seechem De Nitrate in chamber two @ level 2. There is no direct path for water to pass from chamber one to chamber two at the 1st or 2nd level, which limits the flow and I'm hoping De Nitrate has an environment conducive for anaerobic bacteria to complement the aerobic bacteria in the first chamber.
I didn't seek to increase the flow in the Return Pump, which would also have a greater influence on the variation of heights across the three chambers. I have a small power head that pushes 1000 lph, to add to the main aquarium to stir things up - if required. I also use it for mixing my salt water.
Similarly, I didn't seek to decrease the flow in the Return pump, which would reduce the variation in heights across the three chambers and it's very difficult to find a "weak" pump that pumps much less than the "quoted" maximum rate of 200 lph for De Nitrate to operate anaerobically.
Overall, I don't think the variation in height across the three chambers is an issue. The suggested way to top up evaporation water is in chambers two or three whilst monitoring the overall aquarium fill height and the pump ON - no surprises there.
I do have the plug in chamber two. Some folks see this as taking a risk with levels varying but I don't see these getting out of hand. With the InTank Chamber Two, the back wall of the InTank effectively closes off this hole (to some extent) anyway.
If I was to dose activated carbon, I might be tempted to temporarily remove the Water Director (weir) because it increases the safety margin between everything "working" and there being a "problem", but compared to the original Fluval part, it's a great addition.
Simon.
