expanded clay (hydroton, hydroballs etc) as a substrate or filter media?

I picked up some expanded clay (a 2.5 lb package of hydro balls for now) as a bio media and was wondering peoples experiences with it. When searching I saw that one member here has recommended it several times. Others said they were going to try it so I was wondering how well it worked (I'm going to try it but I'm just curious). A couple of filter manufactures use it and one claims that it far outperforms ceramic (of course you can not always trust manufacture claims). I haven't ever used ceramic either for a frame of reference but just wondered how they really compare. There seems to be little info on it being used as a filter media. It will be used in the carbon chamber of a marineland hot magnum canister filter).

I also was thinking of using some in the substrate (not sure if I have enough right now depending on what I decide to do). I have heard mixed things. Some say it floats, some say some of it will float (maybe it depends on the brand). Others have said that it is so light the fish can push it around. Plant roots can grow into it so it is supposed to be good for anchoring plants (and I have live plants). Originally I was Just going to mix some in with the gravel, but I'm thinking of a project for a never siphon tank (except for water changes but not to clean gravel). Basically a home made under gravel filter attached to a reversible pump with pvc pipe and some sort of cover (drilled plexiglass?). With water flow sucking into the gravel, it would get sucked down, up the tube, out of the tank and into a home made canister filter designed for large particles (perhaps with a little siring of the gravel to help). With flow the other direction it would blow stuff up and out of the gravel into the water to get picked up by the main filter (the large particle filter would be secondary to a regular filter). I plan on using it as bio media in my filter soon (maybe tonight or within the next couple of days) but the under gravel filter is just in the idea phase.

I did get another idea. In a terrarium, hydro balls (expanded clay) is used as the bottom layer of the substrate. You put a layer on the bottom and then a separating mesh layer, then the rest or your substrate. It basically creates an underground water table that is a bio filter. The package tells about using a water fall (basically water soaks down to the bottom and then is pumped back up creating a water fall). It got me thinking about the same thing in an aquarium? The same reversible pvc pipe water jets surrounded by expanded clay, a separating layer (maybe still plexi glass or something that will let large particles through), and gravel on top? Basically its a high performance under gravel bio/power filter to supplement a regular power filter and deal with junk built up in the gravel (I was thinking of a minimal air flow under it to keep things aerobic). This would be something that could be turned on and off, not ran all the time (maybe). I guess I could use a smaller pump or air to get flow through it all the time, but I want a powerful pump for fast gravel cleaning that I would probably not want to leave on all the time.


So does anyone have any comments on the expanded clay performance as a bio media, as a substrate additive, or my crazy under gravel filter idea? The under gravel would be tested out in a 55 gal corner tank (that is currently running with fish in it), so I'll probably build it a little here and there outside of the tank once I nail down a plan, and then when ready to use I'll install it.

@garyfla, thanks for the info. I read up on plenum and false bottom systems and found lots of useful information. While a plenum isn't quite what I was looking for (I think, I'll read up on it a little more) it gave me some good design ideas. I understand a reverse flow under gravel filter but how do you incorporate a purge? Are you talking about a bottom drain drilled into the tank or something? I found lots of useful info searching false bottoms too. I assume that to clean on both sides, you need a portion of the false bottom not burred under the substrate or perhaps at a higher level with little substrate on top so you can open a hatch, or are you just talking about snaking a tube or something under it to clean?

@ozymandias, I just tested some of mine and about half floated. I was wondering if it would stop floating once it absorbed water (guess I'll find out as I have a little dish of it sitting). Originally I had just planned on mixing with gravel. I read that some had done it and it worked well to anchor plants as the roots could grow into it. I have no idea if they selected the ones that didn't float or what. I also figured if bacterial in the gravel was good, then more bacteria in the gravel with some of this added might be better. Of course I later modified my plans. I was thinking along the lines of an under gravel filter with some under the filter as an additional bacterial filtration layer. It might actually be better if it floats as it will not get trapped on the bottom in a layer of sludge (not that there should be a bunch of sludge anyway). Its trapped under the filter anyway. If possible, I was still thinking of doing both (in the gravel at least around plants and under the filter).

Conceptually, this is what my current ideas are except something home made and perhaps a little more elaborate.

http://www.ebay.com/itm/27071672564...XX:IT&_trksid=p3984.m1436.l2649#ht_4930wt_952


Maybe something that could be ran all the time as a reverse flow undergravel filter, and ran occasionally like the one on ebay to clean the gravel (basically stir up the gravel and let all the junk get sucked down and into the filter). Perhaps a dual pump setup. A smaller pump or power head for constant reverse operation, and a more powerful pump for occasional gravel cleaning using operation similar to the ebay one. I have a 12v marine pump that is capable of 300 gph at 50 psi with a 35 foot lift for quick cleans (probably have to actually limit power with a bypass as that's probably too powerful). It's not designed for 24 hour operation though. I was thinking a home made canister filter designed for large particles for the quick clean.

I didn't really have a solid plan in place but some of the info found about false bottoms will probably be useful.

You are probably right about my over complicating it. I could probably throw some hydroton under an under gravel filter, and silicone the feed of a canister filter to the tube. When actually building it I'll probably wind up with something in the middle between simplest thrown together and over complicated. As I probably will use pvc pipe though, its very adaptable so it can always be expanded or modified. Its not hard to add a t here or a y there or a valve to alter flow direction, add a second pump or whatever. As far as canister filters I was also thinking simple. A trap prefilter (wide pipe with inlet in the middle, outlet at the top and let gravity pull big stuff to the bottom, maybe with a screen to help) which could always be added to they system later. For a large particle filter, a wide pipe with caps cut just long enough that it would squeeze on the ends of a pool filter, with inlet on the side and outlet in the middle of an end. I imagine I'll build it a bit at a time, and skip or redesign any parts that seem to complicated or expensive to build.

I really don't have any idea if there is an advantage to hydroton over sand or regular loose clay in the substrate. I would think it would have an advantage over regular gravel because it can hold a lot more bacteria. More bacteria means more biological filtration (if you are trying for bio filtration in the substrate). From the sound of it I like the way yours is set up. Mine might be something similar (I guess I'll find out when I actually build it.

Just in case you were not aware of the advantage of hydroton (when used as a filter media and maybe in a substrate, I really don't know). When they make ceramic or porcelain or terra cotta pots or anything that is kiln baked (generally at over 1000 degrees), they try to avoid thick areas or trapped pockets of air and or water. Under the high heat it can cause the item to explode in the kiln due to the pressure of expansion. They are generally dried before being baked in the kiln. If I understand right, expanded clay (hydroton is one brand of expanded clay), they kiln it while still wet with about 30% water. They actually put it in as a mash so to speak into a rotary kiln. It is formed into balls in a lower temperature part of the kiln and then the moisture causes it to rapidly and explosively expand in the higher temperature part of the kiln. It creates a porous structure with a super high surface area. More surface area means more area for bacteria to grow, which means more bio filtration.

I really have no personal experience as far as how well it works but it is used on an industrial level for water filtration due to its ability for high performance bio filtration.

Slappy*McFish said:

It is an excellent bio-media and relatively inexpensive. (You can buy a lot of Hydroton for $10.) It can be used in HOB filters if bagged, but works exceptionally well in W/D filters and canisters.

Click to expand...

Thanks for the info. It was actually some of your posts (from a couple of years ago) that I found searching which led me to post here. Just an fyi for anyone looking for it. Unless the information I have found is incorrect (which I doubt as there are several places that say it), the plant in Germany that made hydroton went out of business and hydroton has been discontinued. There is still some to be found but if you can't, not to worry as there are several other manufactures that make it under different brands. It is all the same thing, expanded clay. Home depot had hydroton (maybe some stores still do) dirt cheap compared to other sources I have found (none here locally and discontinued on their site) but you can still get it pretty cheap (certainly for a small fraction of what ceramic and other medias cost). The stuff I got is zoo med brand hydro balls. Many pet stores carry it including petsmart. It is meant to be a terrarium substrate. Petsmart is kind of high though. They want 10$ for a 2.5lb bag (home depot was about 9$ for 10lbs for hydroton which was the cheapest I found anything). My small town local fish store said they could order for 7$. One place a little further away ordered some for 5$ for me (I had to go out there anyway). As far as other brands or bigger bags, not a single garden center including nearby larger towns had any or could order any (maybe because hydroton was the common brand for growing centers?). Every single hydroponics supply I called either had it or could order it though. Prices seemed comparable to the 5$ price I got on the hydro balls but perhaps you could find it cheaper in a bigger town. It's available lots of places online but shipping is high (unless you want a lot or other things as some places had free shipping over x number of dollars).

One thing that I think might make the hydroballs a little better for filters is the size. From what I have found, expanded clay comes from the factory in sizes ranging from 2mm to 36mm. Hydroton and lots of other brands claim 8-16mm size. The hydro balls are more like 6-8mm. I'm just guessing but I think the smaller size might be easier to deal with in some filters.

Just google "expanded clay" and you will find lots of brands of it. I have no idea if one brand is better than another but so far as I know its all pretty much the same stuff, made the same way. The hydroballs are made in norway.