Undergravel Filter Maintenance

My nitrates and GH are rising and I have green spot algae. Daily 20% water changes. Haven't been gravel vacuuming because of the advise of my LFS guy. He said only vacuum once per year at most and only if I see debris on the bottom. Yesterday I did a deep gravel vacuum.

I took about 30% of the water out via deep vacuuming, scrubbed the glass, replanted the plants, and tested the water. Everything is normal it seems. The water is a little cloudy. I gave it a dose of easy green the nitrates are about 10ppm after.

Honestly there was very little debris in the substrate. I had a little gray filth, but not much. For what I got out, it wasn't worth doing. When I went into the areas with oyster shells, it brought out "white powder." When I had a HOB filter years ago, gravel vacuuming used to reveal major build up of filth, so I know what it looks like when vacuuming with a different filter type.

Not many people have experience with undergravel filters these days...me included. I wonder if I messed up doing this. I added stable to the water to make sure I don't have an ammonia spike. The LFS guy said he has been using undergravel for decades, so I guess I'll just listen to him going foward.

My plants have really built a nice root system in the gravel. They don't look good with all the green spot algae on them, but they are very healthy and dark green. I like how I re-positioned them now...hides the riser tube now and all the roots are below the gravel. I took the opportunity to trim the moneywort and replant the ends that were getting too long. It's a jungle in there.

I ordered a phosphate test kit from Amazon. I think the spot algae is from high/low phosphates. I think the rising GH if happening from the Oyster Shells I put in the substrate to buffer. Betta and Mystery snail seems happy. I'm going to get a nerite snail this week to help deal with the algae.

Question, should I trade in the mystery snail for the nerite, or just add a nerite? I need some help to get the algae off the plants and this lazy mystery snail isn't doing his job. If I drop a piece of cooked spinach in, he'll lock onto it for hours...but doesn't work hard to clean up the tank...that's why I hired him.

 

I grew up with undergravel filters. They work great, but over time they can become a NITRATE nightmare because all of the waste collects under the plenum. What I used to do once or twice a year was to perform partial water changes by vacuuming water out of the riser tube. I went to the hardware store and rigged me some PVC fittings to fit the riser tube and my siphon hose. You would not believe the dirty water that I drained out during PWCs. Anyway, I only did this once or twice a year and this kept the tank nice and healthy for years.

 

I grew up with undergravel filters. They work great, but over time they can become a NITRATE nightmare because all of the waste collects under the plenum. What I used to do once or twice a year was to perform partial water changes by vacuuming water out of the riser tube. I went to the hardware store and rigged me some PVC fittings to fit the riser tube and my siphon hose. You would not believe the dirty water that I drained out during PWCs. Anyway, I only did this once or twice a year and this kept the tank nice and healthy for years.

That's a great idea...I can easily rig something up. The bottom of my tank is clear, no debris under the plate that I can see. But I have 2-3 inches of gravel, so I wouldn't expect anything to make it under the plate.

I was surprised to see how little build up was in the substrate after a couple months of no vacuuming. I plan to do shallow vacuuming once in a while going forward, but I will leave the deep gravel undisturbed until I see congestion. With deep gravel against the glass, I can see if I have debris blocking the water flow.

 

You can google reverse flow power heads for UG Filters. You basically put a sponge filter on the intake of the power head and it blows water down the tube and up through the gravel. This way you’ll have a sponge filter for cleaning the water and your undergravel plates don’t clog up with fish wastes.

 

That's a great idea...I can easily rig something up. The bottom of my tank is clear, no debris under the plate that I can see. But I have 2-3 inches of gravel, so I wouldn't expect anything to make it under the plate.

I was surprised to see how little build up was in the substrate after a couple months of no vacuuming. I plan to do shallow vacuuming once in a while going forward, but I will leave the deep gravel undisturbed until I see congestion. With deep gravel against the glass, I can see if I have debris blocking the water flow.

Over the years the debris will build up under the plenum plate...it takes time. But I will say that undergravel filters work great.

You can google reverse flow power heads for UG Filters. You basically put a sponge filter on the intake of the power head and it blows water down the tube and up through the gravel. This way you’ll have a sponge filter for cleaning the water and your undergravel plates don’t clog up with fish wastes.

EHEIM makes a reverse flow undergravel-cainster system.
EHEIM undergravel filter

 

You can google reverse flow power heads for UG Filters. You basically put a sponge filter on the intake of the power head and it blows water down the tube and up through the gravel. This way you’ll have a sponge filter for cleaning the water and your undergravel plates don’t clog up with fish wastes.

My tank is so small, it would be interesting to see what kind of powerhead I can do reverse flow on. probably a lot of filth would cloud the tank for a while.

 

From my experience with undergravel filters, when people say "only vacuum once per year" they are referring to "under the plenum plate. You still need to get out solids that stack up in the gravel or on top of the plenum plate. If you don't get this stuff out for a year, your water quality is going to decline as it breaks down.

You biological filter is meant to break down ammonia and nitrates, it's not meant to break down solids, it can over time through decay, but those solids breaking down become nitrates trickling to the water.

Now there's plenty of folks that don't look at nitrates, don't even care about them, and have no problem letting a years worth of fish poop build up and break down in their tank. some plant extremely heavy to manage it.
the whole point of an undergravel filter is to use the substrate and under it, to house the beneficial bacteria, for it to work there has to be flow though the gravel. if a spot gets cleared out to the plate it becomes the path of least resistance and the water just passes though in that area, if the plate gets jammed up on top or underneath with detritus/fish poop, the water bypasses those areas and goes the paths of least resistance.

Contrary to some beliefs, the mulm or detritus under the plate is unnecessary to maintain the biological filtration. If it's there, certainly bacteria will colonize it. But if it's not there bacteria will colonize the plate and the glass underneath the plate and the substrate itself. the waste and dirt,,,, totally unnecessary for it to perform as it should, and will jam it up/ block water flow and transportation of oxygen to the bacteria over time, which is where the "vacuum once a year" comes from, because it will take a year or two for fine particulates collecting under the plates to get so thick it blocks the flow.

I don't suggest going and vacuuming the entire bottom at one time, but to alternate half the tank then half the tank every so often when you see your nitrates rising, and a water change not really affecting it. the"white cloud water" comes from disturbing the biological filter. It will settle in again. it will be even less if you do it in sections at a time and not the whole thing at once.

the waste is either going to collect on top of the plenum plates in the gravel or break down and get sucked in under the plenum plates and build up there. either way that's nitrates, phosphates, potassium ect. waiting to break down and become part of the water. I have no idea how much you'd need to plant to use up the waste products and just leave behind a dirt that's depleted of nutrients, but that would be an option to keep nitrates and and stuff down instead of vacuuming.

you certainly can "not vacuum" an under gravel filter, but when you do, do it, because it jammed up and have to, a whole lot of your biological filter will be coming out with the gunk that builds up under the plates because it's colonized that gunk. It's kind of a pain to clean an undergravel filter when it has to be done, it requires a full tear down. and restart basically.

Anyways, best of luck to you however you want to handle it. there's different schools of thought for undergravel filters. None are necessarily wrong.

 

The issue with the reverse flow system where one simply places a reversible power head on the standard uplift tube is lack of surface agitation and therefore gas exchange. The fancy Eheim system posted above addresses this concern with a spray bar at the surface.

If attempting a RFUGF I certainly would advise some other means to break the water surface via an air stone or another pump.

Regarding the build up of nitrates in an unvacuumed substrate: The system is a whole. The level in the substrate (or any filter) will leach to the water and they will always be equal. Regular water changes will always reduce it. The idea that an untended filter can hold nitrates and release them at some later date doesn't add up. Regular water changes can keep it in check.

 

Regarding the build up of nitrates in an unvacuumed substrate: The system is a whole. The level in the substrate (or any filter) will leach to the water and they will always be equal. Regular water changes will always reduce it. The idea that an untended filter can hold nitrates and release them at some later date doesn't add up. Regular water changes can keep it in check.

I disagree here, There's a difference between solids and dissolved solids. You can remove the dissolved solids from the water by water changing, if you don't remove the solids, they sit there in the substrate, or the filter sponge, accumulating and eventually dissolving and becoming part of the water chemistry. it takes roughly 7-8 days for solids to break down by 25%, 18 days for solids to breakdown by 75%, 30 days to break down by 100%. By only water changing. those solids are sitting there, breaking down and becoming part of the water.. I'm not suggesting the substrate or the filter is holding nitrates, I'm suggesting it's holding solids, solids that become nitrates and other things also.

I witnessed it myself on a bare bottom tank with a sponge filter doing daily water changes and bottom vac. Kind of a different than normal situation though, it was 3 months of about 100 angelfish fry growth. not just one or two or a handful of fish.
Yes I'd remove nitrates by water changing and keeping them down by vacuuming out the solids on the bottom, however they would be right back and more, day after day getting higher. I was keeping them low from 5ppm to 2.5ppm, but it was creeping upward after every water 50% water change, Yes daily the fish ate, and daily the fish pooped,and grew, and pooped more. I get out what I could of the solids, but there were still particulates.

The moment I rinsed and squeezed out the sponge, I got back control over the nitrates again. I could keep it at 5ppm and lower again there wasn't a pile of particulates breaking down every day decomposing in my sponge filter anymore.

I can just attribute it to the bioload growing as the fish did, and so the nitrate pile growing, but this doesn't explain the significant drop and ability to decline the nitrate levels, the control regained over it, after squeezing out the sponge and removing what the sponge had caught and held onto. there was the daily nitrate production, from ammonia directly to the water. but there was also solids I was removing with the vac off the bottom, what I wasn't doing was cleaning the sponge of the fine particulates it was catching. the sponge was trickling nitrates into the usual pile as what it held built up and broke down month one and month two, and when I squeezed it out, The gain and rise of nitrates I was experiencing, that seemed to increase subsided back to what I expected there to be fore the bioload. and what I removed daily again.

I'm sure If I left the poop on the bottom for 2 months, nitrates would have been even higher and less manageable through water changes. What I know is removing the solids before they decompose and become dissolved, keeps it out of the water chemistry.

 

The issue with the reverse flow system where one simply places a reversible power head on the standard uplift tube is lack of surface agitation and therefore gas exchange. The fancy Eheim system posted above addresses this concern with a spray bar at the surface.

If attempting a RFUGF I certainly would advise some other means to break the water surface via an air stone or another pump.

Regarding the build up of nitrates in an unvacuumed substrate: The system is a whole. The level in the substrate (or any filter) will leach to the water and they will always be equal. Regular water changes will always reduce it. The idea that an untended filter can hold nitrates and release them at some later date doesn't add up. Regular water changes can keep it in check.

I'm doing 25% water changes every day. It works pretty well for me as I use the water for my balcony plants...they are thriving with all the nitrates. With a 2.5 gallon tank, I just scoop out 4 plastic cups of water, then top it back up every day while testing the water and feeding the betta.

I'll keep an eye on the substrate. It wasn't congested before, but I expected to see more filth come out when I vacuumed. Nitrates shoot up everyday... It's okay as long as I keep up with the water changes. Otherwise it might get out of hand if I stopped changing the water.

I read low/high phosphates can stop the plants from using Nitrates. Once my test kit arrives I'll have a better idea what to do with that. I have easy green I can dose regularly if needed to stop this spot algae.

I think the betta has doubled in size over the last three months. He's kinda lazy...lays around in the plants a lot until he sees me...then swims to the top hoping for food. I limit him to 4 pellets per day...he'd eat more, but then his belly is too swollen. It only takes him about 10-15 second to eat. I soak the pellets before feeding him.

 

Thanks for the explanation, SJ. It makes sense.

But eventually those wastes do dissolve and enter the water where they do get removed with PWC.

Lots of people here never vacuum wastes from their substrate, and many go 6 months or even a year before removing them from the filters. So the wastes are still in the system just as proposed here. I suspect it would depend on the specific tank and WC frequency and amount as to how much extra nitrates were to develop in these situations over time. For the record, I favor at least semi regular vacuuming on all my tanks, UGF or not. I think it's healthier for the fish to get the wastes out. Not doing so can allow bad bacteria to develop and can contribute to illness.

 

Thanks for the explanation, SJ. It makes sense.

But eventually those wastes do dissolve and enter the water where they do get removed with PWC.

Lots of people here never vacuum wastes from their substrate, and many go 6 months or even a year before removing them from the filters. So the wastes are still in the system just as proposed here. I suspect it would depend on the specific tank and WC frequency and amount as to how much extra nitrates were to develop in these situations over time. For the record, I favor at least semi regular vacuuming on all my tanks, UGF or not. I think it's healthier for the fish to get the wastes out. Not doing so can allow bad bacteria to develop and can contribute to illness.

agree. it's dependent on what a person is doing. A person with a low bioload and a lot of water volume might get away with not cleaning waste from substrate or filters for a long while. and yes, water changing will remove the dissolved solids and it all become dissolved solids in time and given enough time, it's "normal" and becomes unnoticeable, it's what you build in a week or two or a month. But in my particular case, I was trying to keep nitrates low to non-existent for the fry development. And it worked for the first month doing what I was doing, but then the nitrate creep started happening in the 2nd month. and the only place it could have been building up/storing up to release was in the sponge from fine particulates.

A person with a lot of plants might want to keep that stuff in there and keep adding plants to counter it building up, plants are just not my thing but as I understand it, it's possible to hit a balance of plant and waste/nutrient release... at least until the stocking grows or shrinks or the plants grow or shrink.

I agree with waste contributing to illness, or transmission of illness in the case of parasites. I hate when my fish eat off the bottom of the tank....you poop there buddy! LOL However, I do understand folks wanting to keep some in their tank for plant fertilizers also. Not, I, but I get it.

 

agree. it's dependent on what a person is doing. A person with a low bioload and a lot of water volume might get away with not cleaning waste from substrate or filters for a long while. and yes, water changing will remove the dissolved solids and it all become dissolved solids in time and given enough time, it's "normal" and becomes unnoticeable, it's what you build in a week or two or a month. But in my particular case, I was trying to keep nitrates low to non-existent for the fry development. And it worked for the first month doing what I was doing, but then the nitrate creep started happening in the 2nd month. and the only place it could have been building up/storing up to release was in the sponge from fine particulates.

A person with a lot of plants might want to keep that stuff in there and keep adding plants to counter it building up, plants are just not my thing but as I understand it, it's possible to hit a balance of plant and waste/nutrient release... at least until the stocking grows or shrinks or the plants grow or shrink.

I agree with waste contributing to illness, or transmission of illness in the case of parasites. I hate when my fish eat off the bottom of the tank....you poop there buddy! LOL However, I do understand folks wanting to keep some in their tank for plant fertilizers also. Not, I, but I get it.

Sonic the Betta doesn't eat off the bottom. He's such a pig that he finishes off all the added pellets in seconds...floating pellets and none last long enough to make it to the bottom. I have seen some of his poop on the bottom from time to time, but the Mystery snail gobbles that up... I don't know what snail poop looks like...haven't notice any of that.

It's clean on the bottom of my tank. I don't know if it will always be this way. My tank has been cycled for less than 6 months. I don't overfeed and don't have a heavy load of fish. I have a lazy betta with a snail that cleans up after him.

I need to know where my phosphates are to have a plan what to do about this green spot bloom.