Juwel tanks with their internal filters are very popular with those who keep discus in a planted tank.
Before
The juwel internal filter is a perfect example of german design. Water enters the filter from a number of opening across the filter body. The filter medi
is held in two parts by two plastic cases which ensure a gap between the two groups of filter medium. There is two exit holes which feed the water to the internal powerhead back into the tank.
This set up ensures the following
> maximum water intake with little chance of blockage and some surface skimming
> one block of filter media with a high turnover of water through it ensuring high speed mechanical/chemical /bilogical filtration.
> a second block of sponge media with a slower throughput of water ensurehigh quality biological filtration
This is fine and works very well. However I have experimented with some changes which require nothing to be altered or cut and glued in in anyway, maintaining your warrenty.
How to improve the filter
Step one
Remove all filter media and the two plastic baskets which hold them. You will not reuse the carbon and nitrate sponges, in a planted tank they are not good things to have.
Step 2
Fill a filter bag such as a 3ltr SERA filter bag with your choice of biological filter material. I used a larva based material and some old efimeche. I easily filled a 3litre bag and the filter chamber still looked empty, you must use a filter medium bag as trying to take loose filter media out of the filter any reason is just not fun. Place this back in the now totally empty filter container.
Step3
Block the middle water exit (marked A in the after diagram) this will ensure all water will travel the full distance through all filter media. I achived this by using a small flat piece of flat plastic which was kept in place by the weight of the replacment biological filter medium.
Step 4
Place a small amount of sponge down the back tube area (marked B in the after image). This will reduce the inflow from the slots in the back of the filter body, leading to a higher flow rate through the inlet next to the heatersat giving improved heat distribution a little.
Step5
Place a filter wool pad ontop of the new biological filrer material, then place a Juwel sponge ontop. You will still space enough to place yet another juwel filter sponge ontop. This will further increase the amount of bio filter material.
Do not place a filter wool pad on the top, placing one or more sponges on top will increase the life of the filter wool by trapping medium to large waste material as it comes inot the filter.
The end result.
An internal filter with more bio mass than all but the largest externals, a
standard Juwel will give you 3-4 litres. Filterwool pad that lasts much longer.
A slight reduction in the flow output leading to a more efficient bilogical filtration (slower is better). Water flowing over much more filter material (as you block the middle filter exit hole 'A'). More water flowing over the heaterstat, giving a more stable heat level.