Fish bioload, extra filtration, heavily planted?


Guru Class Expert
Jun 26, 2008
Albany, California
I know the 1-inch of fish/gallon rule is loose and has a lot of controversy around it. And also that most planted tank enthusiasts almost always err heavily to the conservative when it comes to numbers of fish per gallon. But just how much does having a good numbers of plants and heavy filtration mean you can add more than what might be conservative amounts of fish?

I have a 72 gallon with two eheims, a 2026 and 2027, and am likely going to add a Rena XP3 (because I just got one for free). That will give me a huge amount of flow and water filtration which can only help in keeping the water clean from fish waste, etc. I also have a fairly heavily planted bioload with a good number of stems, floaters, and also anubias, ferns and so forth. My Rotala macranda, Tonina fluvatis and some other plants considered "challenging" grow well and pearl excessively. I am using pressurized CO2 with an in-line PVC CO2 reactor. My two drop checkers (one from Cal Aqua with their indicators soultions, one Red Sea one in which I use 4dKH water) are both a nice lime green. I have a Koralia 2 helping with dispersement to keep CO2 flowing around the tank. I follow a basic EI fert regime for my size tank. I have not had any serious algae issues in some time now (couple of months?) maybe the occasional BBA on outflow pipes, some minor GSA on old leaves and on the glass, and some GDA algae sometimes (though the latter has not re-occured for over 3 weeks now).

I do however have a good amount of fish: 4 rainbows, 3 pearl gouramis, about 40-50 tetras of a few varieties, about 15 cories of a few types, 2 SAEs, 2 BN plecos, 5-6 ottos and a farawella, most of which I have had for close to a year now. I know this is high fish count but while my nitrates and phosphates are on the slightly high side (20-30 ppm and 5 ppm, respectively) if I back off either N or P with my EI fert regime my plants suffer so I keep dosing that even though my fish bioload keeps them high as well. I have not had any fish loss in a long time and my card tetras are bright and colorful, my rummy-nose is bright red on his nose, and overall the fish seem really active, healthy and colorful with little stress that I can see.

So, my question? Should I get rid of the rainbows and/or gouramis and strictly stay under the 1 inch/gallon rule? Or since things seem to be so far so good not worry about it?

Tank is here if any one cares to see:
My 72 gal rimless (10/12:added photo with plant number ID)

Tom Barr

Staff member
Jan 23, 2005
I think you might want to sit back and think about what the tank will look like with all tetras and cryptic species like plecos etc. Is that a goal you'd like?

The test kits measure total, not bioavailable N and P.
So some fish etc should be considered as part of the plant food, but not that much.

With higher fish loads, I tend to do more/larger water changes.
This resets the fraction of N and P better to the inorganic side.
Fish like it and Albany has soft water with a little PO4 in it.

PO4 need not be 5ppm , but then again, have you calibrated these test kits also?
Start there.

Then if so, try dropping the NO3 to about 20 and the PO4 to about 2-3ppm. the target is 10-30ppm of NO3, but ideally, about 20 seems like a good medium/average.

Keep traces high, add GH booster etc.
Clean filters often.


tom Barr