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To Fertilize, or Not to Fertilize, that is the question

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I have two tanks that have algae problems (surprise surprise) to some degree, and I've been doing around 40% water changes every week to keep it at bay. The two tanks are:

5.5 Gallon with Finnex Stingray for 6 hours, nitrate testing at zero. Crazy hair algae and cyano that I have to pull every week. 6 Emerald Rasboras, and  snails.

20 gallon long with Finnex Stingray for 9 hours, nitrate testing at around 10 ppm. Algae isnt as bad, just some BBA will build up on large flat leaves of anubias or such if I miss a week. 10 Red Eye Tetras, 1 Electric Blue Ram, a whole smattering of Kuhli Loaches, Amano shrimp and snails as algae control.


I'm attaching a picture of today's nitrate test for context, this is a week after my last water change, no fertilizers. (Left is 5.5 gallon, right is 20 gallon). The question is, should I stop being such a nut about water changes and adjust with fertilizers and light instead? I tried being hands off with the 5.5 gallon but the hair algae just goes bonkers. If I skip a week on the 20 gallon, there's definitely a noticeable buildup of algae. Unfortunately I don't think I can cram in any more clean-up in either tank as they are bit full on stocking I think. Thanks in advance!


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If you've got plants in thank small tank, I would definitely start dosing ferts. 0 ppm nitrates is going to leave your plants unable to use any of that light energy coming in from your stingray, so the algae are going to have a field day. Water changes are a treatment for symptoms, but they will never address to core problem. 10 ppm in the other tank is pretty solid, but if you've got plants and 9 hours of light, you could afford to push it up to 20 ppm and it will make your plants more productive, which will then make your algae less productive.

A 40% water change per week is a lot, so if you are able to address the algae problem through boosted ferts, I would do it.

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The 5.5 Gallon: Room Temp, 7.4 pH, and has been up for 8 months, last addition of livestock was 4 months ago. Some plant growth.

The 20 Gallon: 82 degrees, 7.0 pH, has been up for a year, 6 months since last addition of livestock. Slow plant growth, and stem plants oddly never survive..

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It sounds like you definitely need fertilizers if those tanks have been established for that long and you are still experiencing algae growth. Get those ferts in there and it should help a lot. Also, try root tabs if your stem plants aren't growing. What species of stem plant are you trying to grow?

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On the 5g I’d temporarily add some Amanos and a few Otocinclus. 

On the 20 I’d temporarily add some Otocinclus or trade out a few of the Kuhlis. Also,  decrease the amount of time you’re running the light

For both tanks follow the great advice already posted and add fertilizer. 

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