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Undergravel filter, high pH, nitrates, and algee question

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I've been keeping aquariums for about 37 years now, but this past spring I decided to change it up a bit and decided to try a planted aquarium.  Since doing so I've had a really hard time keeping the nitrates in check.  I have some thoughts on what may be occurring, but I thought I would post here to see if anyone had other thoughts.  The aquarium in question is a 29 gallon aquarium, standard aquarium gravel with an undergravel filter, a HOB filter and a small canister on it.  Historically I've been able to keep the nitrates in check with water changes and throughly vacuuming out the gravel.  When I first put plants in I did the rookie mistake...I put easy green in once a week, added a few toot tabs, cranked up the light, and since i use soft water and have a few mystery snails in the aquarium i add Seachem Equilibrium to the aquarium....all said and done, i did an awesome job growing algee.  Since then I turned the light back down, stopped putting in easy green and root tabs.  I do still use the Seachem Equilibrium and every day or 2 I hit it with Easy Carbon.  By doing that the algee is better under control, but the nitrates are still going nuts, measuring 100-200, even with 70% water changes each week.  The water here is very high pH, 8.4.  The aquarium is fairly well stocked with smaller fish, though not more than I have historically done.  It's mostly platties, cories, a bristle nose pleco and clown pleco.  I am questioning the test a little and wondered if any of you have ran into test strips misbehaving if you have high pH soft water and add Seachem Equilibrium to the water.  In many instances the fish don't behave as if the water is high nitrates, but there have been some instances over the past couple months where they got more sluggish and didn't deed as well as they usually do...so I'm not totally convinced the test is bonk, though when I test the water in those instances it still shows 100-200 on the test strip.  Now there are a few factors that may be at play that may be making it harder to get my arms around this nitrate issue.  The first is that with the live plants I can't vacuum up every inch of gravel on a weekly to biweekly basis like I use to do.  Second, I question if the undergravel filter makes life with plants harder since it basically equalizes the nitrate level out over the entire water column, thus overall it's higher on average, where as if you don't have an undergravel filter you could actually get a huge gradient of nitrate levels going from just above the substrate down to the bottom of the substrate.  Thus your rooted plants could get a huge dose of nitrates while still letting your fish swim around in lower nitrate water.  Where as with my undergravel filters (which I've used in everything since the 80s) the circulation from top to bottom just evens everything out.  A third thing I've noticed is that since using the easy carbon my HOB and canister filter doesn't plugg up like they use too.  It use to be every 2 weeks I would have to clean off the sponge in my HOB and every 6 weeks go through the small canister cleaning it out and there would be a layer of gunk on it.  Since using the carbon there isn't hardly anything on it, which makes me wonder if the gunk has been broken down by the carbon and is holding up in the water column?  Or is it that the gunk was really mostly algee plugging up the sponges.  I've been looking around a bit, but I haven't found a good explanation of exactly what, chemistry wise, happens when you add easy carbon to the water.

Anyone have any ideas of things to try to reduce the nitrates, as I would really like to run my light brighter than I am.  I have wondered if using CO2 would help to reduce the pH some and maybe help the plants eat up more of the nitrates, but I think there are other things I probably should tweak first to get things narrowed in more before adding in another variable to the equation.

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I know personally I could go weeks without a water change and the nitrates would be low. However, I just added eight little fish to my aquarium and about five days later the nitrates were pretty high. It might be the amount of smaller fish you have. You could try removing some of them into another tank if you have one. Also, do you have any water spangles in your tank? These floating aquarium plants absorb nitrates from your water. 

A reason the algae might be growing is that you just don't have enough snails/ fish to keep it in check. I have a nerite snail and about 10 endlers in my tank and surprisingly, they eat algae and constantly clean off my decor and live plants. I rarely ever have to clean my tank glass. 

Do you think you might be overdosing the easy green? I added a little more than usual one week and more algae seemed to appear. Could also be the root tabs. I don't use those, so maybe the mix of tabs and easy green encouraged algae growth. 


Hope this was somewhat helpful! 😅

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That’s strange, after a 70% water change you shouldn’t be seeing 100 ppm nitrates. I wouldn’t think the filters have anything to do with it. I would suspect the test strips might be off. I’d try some new ones or the API liquid test. I’d also test your tap water for nitrates, that could also be the problem. 

You didn’t mention how many fish are in the tank, that might also  have a bearing on the situation. 

Edited by Patrick_G
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My first suggestion is a liquid nitrate test - the strips are great for an overview but there's a wider range of interpretation so not super accurate, and right now you need accuracy.

Even with the ferts I'm a bit surprised you're still that off the charts - 70% WC should be enough to keep things in check....not to mention the plants and even the algae should be uptaking some of it. Again this has me thinking time for liquid testing.

Finally, low hardness and high pH, are you on a well with a water softener system? That's the classic indication of that, and can make your foray into plants a bit more difficult (though you're using Equilibrium, so you're over the first hurdle).

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Canister filters are often called nitrate factories. There's a lot of debate within the hobby as to whether that's true or not. Some insist it's not and that if you maintain a canister filter it's fine. Anecdotal stuff can often be dismissed, but the nitrate factory thing has been around for a long, long time. I'd recommend a thorough cleaning of the canister filter including the hoses and see if that made any difference. It's one of those "can't hurt and might help" things to try out.  You'd be amazed at the gunk that can pile up in a canister filter hose. Hose cleaning brushes are a great investment for a fish keeper.

Other things to look at would be your substrate. Some leach nitrates. Especially substrates made for planted tanks. Plants need nitrates, so the substrate makers figure it won't hurt anything. You say it's "standard aquarium gravel" but there are all kinds of things sold as aquarium gravel. A buildup of debris under the UG filter grid could be an issue also. If the tank has a glass bottom and you've got it on an old-school angle iron stand, a peek up from the bottom can let you see what if anything is under the UG grid.

If all else fails, you can try using a nitrate sponge type of plant like a water hyacinth to suck up the nitrates or add some of the Poly-Filter material to your filtration systems. 

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It's awesome being able to chat with other who enjoy aquariums.  You all have tons of good ideas to look into.  I'll try to answer some of the questions posed in the previous posts.  As of fish, the aquarium is fairly highly stocked for a 29 gallon aquarium, though historically by doing enough water changes and filter cleans I've been able to keep it under control.  Currently it has 6 platties (salt & pepper, sunburst, and red wag platties), 3 corys (2 green, 1 spotted), 1 buenos aires tetra (which has been in there forever and a day), 1 Denison Barb, 1 bristlenose pleco, and 1 clown pleco that you only spot every few weeks because he only comes out when it's totally dark.  Oh, there are also 2 mystery snails that I originally put in just to do work getting rid of algae, but as it turns out my 5 year old, my wife, and myself have kind of been totally taken by the snails.  Every time we look at the aquarium we are constantly looking too see where they are and what they are up to.  I never thought I would find snails in an aquarium really interesting.

I'll attach a picture below of my current layout, both from before and after I converted over to live plants.  

As of using too much easy green, last spring for the 1st month I had plants, I totally used too much, but for the past 2 to 3 months I haven't used any because I haven't been able to get the nitrates down decently.   I am a little concerned though that other nutrients are probably low and that probably isn't helping the plants.  

As if floating plants, I haven't tried those yet, I do have a top on my aquarium so I always figured I would see those much, but maybe the underside of some of the floating plants would be cool.

As of trying a different type of nitrate test, totally a good idea and I'll be ordering some up to compare the strips too.  

As of the water characteristics, you are totally correct, I am on soft water.  The water in this part of souther Wisconsin is extremely hard and has over an 8 pH coming out of the tap.  If I didn't use soft water I would be fighting lime buildup all over, and that has its own frustrations with it.

As of canister filters being nitrate factories, can can totally see how they could become that, especially if you use plugging substantially as the criteria to clean them.  For example on my 29 gallon aquarium I have a fluval 303 canister on it.  I like how it has multiple compartments so I can use all sorts of things in it, and don't need to by anything special for it, aka you can just cut bulk stuff to fit.  But anyways, it has a huge amount of surface area vs what would really be required for a 29 gallon aquarium, so you could run a really long time before cleaning it.  The problem is, before it plugs off, it actually has a lot in it that is breaking down into nitrates, thus if you don't clean that out relatively frequently it's going to cause headaches that it helps with.

Media wise, you can see in the pictures below it's just old fashioned blue painted gravel that I probably picked up at Petco years ago.



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