waterdrop
Enthusiastic "Re-Beginner"
Great idea about the slightly larger tank...
ok, the pond filter is a great way to keep learning more details about filters, media and biofilm cloning topics. The reason you see these plastic objects (they come in all sorts of shapes, often looking like ball shapes) in larger filters (like sump filters for very large tanks or pond filters) is that the best media choice of this type (ceramics) becomes too expensive when used in these volumes, so designers resort to a less ideal material, plastic, to save money. The not so great surface quality is made up for by the massive volume of hundreds of balls in a large volume.
My concern for you trying to use a few of these plastic balls is that when few in number, you are not really getting all that much surface area of bacterial biofilms, relative to something like sponge which has much, much higher surface area when looking at smaller volumes as associated with smaller filters and aquariums. This of course is not to say that -any- mature media going in to a fishless cycle is not good, its always good, it just seems like a good learning thing here.
Now another thought is that -some- day your Mom is going to find that the 3 big sponges in the pond filter have begun to fray and wear out and will need replacing. At that point she will have to go out and take all the necessary steps to talk with the maker of the pond filter and see about getting replacement sponges. You could actually be a help to her by doing that tedious work and documenting things for her in the future. The plus for you would be if you found that you could buy her one of the replacement sponges at a reasonable price, in which case I'll bet you could take scissors or a knife of some sort and cut a chunk of one of the mature ones and replace it with a same(very slightly larger to make it tight) sized chunk of new sponge. People who work with fish do this sort of thing all the time and all of this will be good for her to learn too or the family or whatever. Its better to understand the principles than to just be dependent that there is some fitler out there for her pond that she doesn't want touched until it breaks, lol! Note that you can also be looking carefully at the relative pore size of the 3 sponges as they will probably have different air space within the sponge to trap smaller and smaller particle sizes. Its not too hard to think about this relative to your aquarium filter.
~~waterdrop~~
ok, the pond filter is a great way to keep learning more details about filters, media and biofilm cloning topics. The reason you see these plastic objects (they come in all sorts of shapes, often looking like ball shapes) in larger filters (like sump filters for very large tanks or pond filters) is that the best media choice of this type (ceramics) becomes too expensive when used in these volumes, so designers resort to a less ideal material, plastic, to save money. The not so great surface quality is made up for by the massive volume of hundreds of balls in a large volume.
My concern for you trying to use a few of these plastic balls is that when few in number, you are not really getting all that much surface area of bacterial biofilms, relative to something like sponge which has much, much higher surface area when looking at smaller volumes as associated with smaller filters and aquariums. This of course is not to say that -any- mature media going in to a fishless cycle is not good, its always good, it just seems like a good learning thing here.
Now another thought is that -some- day your Mom is going to find that the 3 big sponges in the pond filter have begun to fray and wear out and will need replacing. At that point she will have to go out and take all the necessary steps to talk with the maker of the pond filter and see about getting replacement sponges. You could actually be a help to her by doing that tedious work and documenting things for her in the future. The plus for you would be if you found that you could buy her one of the replacement sponges at a reasonable price, in which case I'll bet you could take scissors or a knife of some sort and cut a chunk of one of the mature ones and replace it with a same(very slightly larger to make it tight) sized chunk of new sponge. People who work with fish do this sort of thing all the time and all of this will be good for her to learn too or the family or whatever. Its better to understand the principles than to just be dependent that there is some fitler out there for her pond that she doesn't want touched until it breaks, lol! Note that you can also be looking carefully at the relative pore size of the 3 sponges as they will probably have different air space within the sponge to trap smaller and smaller particle sizes. Its not too hard to think about this relative to your aquarium filter.
~~waterdrop~~
The LFS has sold out of filter sponge but are due a delivery of stock soon. The guy says that he gets in massive sheets and cuts it down to size for around £2.99, pretty cheap compared to the £8 tiny box at the pet shop. He also said he will order me some moss balls when I want them, but said that they are just snail breeders and I will be over run with snails. He did then suggest I get some puffers to keep the snails at bay - lol. 
She (i pray for a she, im sure i already have a male lol) will make a good friend for my current Tench
