Rcpilot

I have a 20 gallon tank with an undergravel filter system. I'm using 2 lift tubes and an airpump. It's a double outlet airpump and seams to put out quite a bit of air. It produces quite a bit of current in the tank from the lift tubes, so I'm assuming I have good circulation through my gravel bed.

The actual undergravel plates are not big enough to cover the entire bottom of the tank. Maybe they came from a smaller tank? I don't know. I bought this setup used. It was empty and dry when I bought it.

The undergravel plates can be placed side by side in the middle of the tank. This leaves about 3" of space on the outsides of the undergravel plates, near the glass. So, I have about 6" of "unfiltered" gravel on each side of the tank.

The undergravel plates sit about 1" off the bottom of the tank and I have between 2 and 3" of gravel on top of the plates.

That leaves me with 3" of gravel on each side of the tank and it is about 4--5" deep. There is no oxygen circulating through this gravel. It's not sitting on top of the undergravel plates.

I'm wondering if that gravel is deep enough to create a "seudo" DSB in my little freshwater tank?

I only keep 3 little goldfish in this tank. They started out as babies under 1" and have now grown to body lengths of about 2.5" each. This does not include their tails which are shaped like large fans. Total body length on these 3 fish averages 5" from nose to tail. They seam happy and healthy.

I change about 1 gallon of water per week--because thats about how much it takes to water my 6 little houseplants. Cheap fertilizer--what can I say? The fishies get clean water and the plants are green and healthy.

My routine is to clean about 1/3 of the undergravel filter bed on each water change. First week I start on the right, second week in the middle and third week on the left. Repeat the process. The whole undergravel bed ends up gets cleaned monthly--in a roundabout sorta way.

I've posted a crude paint image of my tank setup. I don't test my water. Not ever. I had 17 fish tanks when I was a teenager. Soooooo many years ago. I had Cichlid tanks over 100 gallons and a 135 saltwater tank. I think I got a handle on a basic 20 gallon tank with an undergravel filter.

It was all undergravel filters and cannisters back then. Wet/Dry was just starting to hit the scene. A lot has changed in the last 20yrs. Now we got this discussion about the DSB and the breakdown of the nitrates into nitrogen gas and POOF!! it's all broken down and outta the tank.

Do I got a poor mans DSB here, or is the substrate too shallow--too large in particle size? Too oxygenated?

Thanks

BJP

I'm going to guess probably not but if it does you should have just enough irregular agitation that the tank develops a bad hydrogen sulfide problem potentially killing the fish. You want have the solid layer above it keeping the gases in check until the second layer of bacteria make it harmless. I'm assuming this is only a temporary tank anyway since a single fantailed goldfish would completely fill it as it grows and you currently have 3.

If it was me I'd yank the UG out, thin the gravel depth down and increase the volume of the weekly water changes. The current schedule is too small to keep the nasty mess that accumulates from building up and eventually blocking flow. The nitrate and DOC levels should steadily rise as well.

If you're feeding flake food or sinking pellets the UG pulls food and waste down into it. By not having it running you can get by feeding less which translates into less food going to waste, increasing nitrate and DOC's and saves you money.

Another option if the plate was full sized is reverse flow using sponge prefiltered power heads to inject clean water down the uplift tubes where it passes under the plate, up through the gravel and keeps food and waste from settling in. The powerheads though would typically cost more than a small hang on back filter for a 20 gallon.

If you're not fond of testing that's fine but I would at least monitor the nitrate. If you do enough water changes to keep the nitrate from accumulating you correct most other problems before they happen. Eventually the growth from the three goldfish is going to overload the tank. You'll know when that occurs when the percentage and frequency of the water changes you're willing to do has been maxed out and the nitrate is still rising steadily.

When you move to the larger tank give a fine sandy bottom a try. The sand allows almost no room for anything to settle in. That allows for easy collection by a filter and cuts servicing down to simple skimming with the vacuum. You can get sand in many colors if that's the look you like and the colors can be mixed to make many looks. You'll have some options for keeping the sand stirred as well including banjo cats, gold dojo's which I keep in my goldfish tanks and horseface loaches. Those little snails that bury in the sand can help as well.

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Rcpilot

These 3 little goldfish have been in this tank for about 2.5 yrs. I've been changing 4 gallons a month for that entire time. A gallon per week. Thats a 40% water change per month on average. But not all at once--didn't want to shock them. I thought I was doing good.

Seams to me that if the hydrogen sulfides were building up, I'd have a rank smellin' tank and my fishies wouldn't be growing and acting healthy, so I kinda disagree with that theory.

I have been thinking of moving back into the hobby on a larger scale. I jst got so tired of cleaning tanks and cannisters when I was a teenager--I got completely out of the hobby for about 17yrs during my early 20s and 30s.

I am intrigued by this DSB method of filtering. I like the idea of having a completely biological filtration system that turns the most dangerous chemical (nitrate) into harmless nitrogen gas that can be bubbled out at the surface. While nitrates used to build up slowly--over time--you always had to do regular water changes to control it. There was no other way to reduce nitrates 20yrs ago.

I've been reading articles and it seams the best size sand is in the .2mm -- .05mm size. Thats pretty fine--almost like silt. Thats what got me to thinking my gravel might be doing some mild work at nitrate removal, but probably not much due to the large granular size of gravel.

Just pondering the thought. I've actually been thinking of getting a Banjo Cat. Sort of a "garbage man" to work the bottom. My goldfish seam to do a lot of grazing on the bottom already. They are big enough now that they can pick up pieces of gravel in their mouths and roll that gravel around before spitting it out and moving on to another piece. I don't know how much nurishment they get from that, but it's what fishies do.

No snails though--I had one of those once and it had babies. HUNDREDS of babies. They get caught in filters and under rocks and all over the place--and then they DIE and then the water is a disaster. I'll NEVER have snails in a tank again. Never.

Thanks for the help. I'm goine over to the SW forums and start doing searches. I'm interested in a big tank again and want to investigate filters for a tank that will house primarily fish. No invertebrates or live rock.

BJP

If you notice my first words were "I'm going to guess probably not". It doesn't sound like you're getting anaerobic development like I suspected. As for the fish though they aren't growing at a normal pace by any means. My fantails are bigger than what you listed after less than six months.The conditions are stunting and slowing their growth. That's one of the hardest things about this hobby to get people to see the difference between what could have been and what they actually have. When you don't have an example in sight to compare to first hand it's easy to think things are going along great.

A simple nitrate test takes all the guessing out. If your water changes are keeping pace it'll show you but what typically happens is something along this path.

Say the tank cranks out 10ppm of nitrate a week. You change 1/20th of the water you leave 9.5ppm of nitrate in the tank. At the end of the second week you now have 19.5ppm nitrate. The 9.5ppm left behind last week plus this weeks production. You change 1/20th of the water and leave behind 18.525ppm nitrate. At the end of the third week once another 10 ppm is cranked out you're now at 28.525 ppm. You change 1/20th of the water and leave behind 27.099ppm nitrate. Add the forth weeks 10ppm addition and you're now at 37.099 ppm nitrate. Change 1/20th of the water and you leave behind 35.74 ppm nitrate.

While you may have changed 20% of the tanks total gallonage in a month, you left behind more than 87% of whatever accumulated.

Play with the math a few more weks and see how far this pattern continues then factor in increased growth resulting in larger increases per week from larger bodied fish and larger food portions and you'll see where we're headed. It's not the nitrate we worry about so much but all the things we can't test for that accumulate at the same time. With a larger tank and water changes sized to what's actually going on in the tank instead of set patterns I would expect your goldfish to be softball sized by now and actively reproducing if you ended up with at least one female.

I rarely see my banjo cats but it is a pleasure when I do. They spend most of their time buried in the sand and come up occasionally to eat shrimp pellets.

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Rcpilot

Well, I'm no math whiz, but point taken.

I'll get a test kit and see where I'm at.

Thanks