Hi Svetlana and welcome to Loaches Online.
Hagen pumps are not the be-all and end-all of aquarium powerheads, but they are highly adaptable and reasonably compact.
The Eheim 1250 is pretty large at 7.1"x3.8"x4.7" and weighs 3.5 lbs and is rated at 28 watts.
An Aquaclear 802 is considerably smaller and uses 20 watts. The wattage will not only affect the power you're having to pay for, but can be a contributing factor in likely water heating effect.
The intake side of an Eheim 1250 is 3/4" so will probably adapt fairly easily to PVC plumping pipe available in Holland I would think.
Unless you have a very large tank hiding a pair of 1250's will be an aesthetic challenge.
"Too much" power is not normally a problem. You do not quote the size of your tank, so determining where you sit in the "too much" area is not possible. In a large aquarium you could be in the "too little" area. With hillstreams aim for a
minimum turnover rate of the tank's capacity of 16 times per hour. 20 times would be even better.
You can only guage this on manufacturer's
claimed pump outputs. The reality may be that they produce considerably less than quoted.
Look at this article
http://www.loaches.com/articles/water-m ... h-aquarium to see the truth discovered during some "tuning" of Aquaclear 802's for instance.
As to the question of how many pumps and their power, it will depend on the width of your tank what you can fit in. Your picture link above isn't working, but is of this filter:
These would make good additional filters, but you'll still need some good coarse sponge filters on the River-Tank manifold intakes as well. I have never proposed that these intake sponges should be the sole filtration in a River-Tank. My 65 gallon tank has two cannister filters in addition to the 3 quite large (4" dia) R/T intake sponges.
Martin.
Resistance is futile. You will be assimilated.
