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Get rid of the zeolite …but slowly, to allow your BB to fully develop. Zeolite is usually only recommended for an NH3 problem, and even then it will function too slowly in a crisis. Let your plants and BB take care of your ammonia (your plants will appreciate it). In any case, the zeolite is not directly causing algae.

My guess is that the removal of the ammonia/nitrate source by the zeolite (probably why your nitrates are dropping) and the addition of the little bit of CO2 you added has destabilized your plants, even though they still appear healthy for a while. pH WILL fluctuate with the addition of sufficient quantities of CO2. One bps is not nearly enough CO2 for that sized tank and bps should not be used as an indicator for CO2 levels. Instead, use a drop checker or, better, compare the pH of fully degassed water (a sample allowed to sit out for a day or two) to fully gassed water. Increase CO2, slowly, until you obtain a full one-point difference between fully gassed tank water and the sample. Make sure that the dKH of both is the same. This will give what is considered the optimal 30ppm CO2 level.

With enough light (which must be stable, as well - get that timer), when you add CO2 you kick your plants to a new level of growth. Often, the current fert dosing regimen needs to be increased as growth may cause the need more. Flourish (old comprehensive), usually does not contain enough macros for a CO2-injected tank.

You don’t need to deep-vacuum substrate in a planted tank, just remove detritus on the surface of the substrate. The nutrients accumulating will benefit the plants.

My 20g has been running for a couple years, and recently got a re-scape and equipment upgrade. Everything is growing in well and all the fish are happy, but in the last 2 weeks I started having major problems with algae.

Tank info:

Light is a Beamswork

Dosing is API Leaf Zone with Iron (10ml/week) and Flourish (2ml/week) plus I put in a couple root tabs under the patches of hairgrass in the corners. Planting is very heavy with a lot of fast-growing stems (pearlweed, rotala rotundifolia, moneywort, and hydrocotyle triparta), plus about 30% coverage of the floor in a combination of DHG, staurogyne repens, pogostemon helferi, and ranunculus inundatus. I also have a baby sword in there that is getting moved out when it gets a little bigger.

Ammonia 0
Nitrite 0
Nitrate 30ppm before water changes (was almost 40ppm for a week or so right after planting, but it's been dropping steadily as plants fill in).
Ph 7.4 (doesn't fluctuate with CO2 due to hardness of water)
KH 7°, 120-130ppm
GH 8°, 140ppm

CO2 1 bubble per second (Ph doesn't swing due to hard water buffering). Tank gets CO2 while the light is on (8-9 hours a day: I have to turn light on/off manually because I haven't ordered a timer yet).

Filter is a Fluval Aquaclear 30 (150gph) loaded with sponge, floss, carbon/zeolite mixture & ceramic biomedia. Filter is mature and only the carbon media bag ever gets replaced, everything else gets gently rinsed 2x monthly in aquarium water.

Substrate is 3 year old Ecocomplete, which is vacuumed during water changes to minimize excess mulm accumulation.

Water changes are 50% weekly now, last month it was 30% 2x weekly when I was waiting out the nitrate spike while the plants caught up.

This tank never had serious algae issues in the past, but since adding zeolite to the filter I've started seeing algae that I have never, ever had issues with before. I'm used to fighting BBA on my mopani, as it loves the hard water and the slow decay of the wood in a tank, and I've seen green dust algae here and there if I left lights on too long too often, and occasionally diatoms if I stirred up a lot of mulm, but I'm seeing thread algae, hair algae, etc. now too. It's not apocalyptic, but I'm not happy about it, and I want to get it under control before it gets too crazy.

All the plants are growing like mad, no signs of deficiencies. The rotala and hydrocotyle pearl like crazy all day, so I don't think plants are failing to take in nutrients, nor are they dying back. Everything is transitioned, and nothing is dropping old leaves anymore (immersed leaves were removed as soon as new growth started), but the algae is gaining ground, not receding. I actually want to thin out the hydrocotyle because it's getting pretty fluffy, but I'm reluctant to remove plant mass until the algae is back under control again.

The 2 things I changed in the week right before the algae started showing up was the addition of pressurized CO2 and changing my carbon out for the carbon/zeolite mix. I'm reluctant to blame the CO2 since that encourages the plants to take up nutrients faster, not slower, and usually helps with reducing algae in a planted tank (I could be wrong here though; this is my first CO2 tank).

I've read that sometimes zeolite can contribute to algae in a tank, but couldn't determine why that supposedly is, and I'm always a little skeptical about what I read online when it comes to tanks if I can't find something concrete to back it up. I suppose I could just dump the carbon/zeolite mix and replace it with plain carbon, but I figured I'd pick everybody's brain to see if I'm missing something else here that is contributing to the issue. I also want to figure out why I'm suddenly getting new types of algae after several years without it.

I did a 2x dose of Excel yesterday and the day before, using a pipette to squirt it directly on the problem spots, but then my shrimp started looking sluggish so I haven't added it today in case that was the issue. I also just did my 50% water change this evening.

Any ideas folks?

2,601 Posts
I don't agree with this assessment of the problem.
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