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Discussion Starter · #1 ·
Hi, I currently have a female sorority tank 18/20 gallon long, but actually measured about 15-16g with substrate, decorations & plants. I also have an aqueon quietflow 10 filter 100GPH. With 8 bettas so far (I keep one floating in a topper because everyone HATES her, until I find a new home :(, I had one small identical one about 4 months ago that was eaten by my bettas) I've had it for about 10 months, and about 3 months ago I got plants. They did well, even in low light, but I soon got brown diatom algae and an ick outbreak. I kept the plants in a separate jar during heat treatment but they rotted & died :(. I got more plants later and I still have the diatom, I NEVER had it prior to adding plants, and my tank has always been cycled, measuring 7.8 PH, 5-10 ppm for nitrates weekly. I think returning to an old jar of pellets (from hikari bio gold to aqueon) caused the diatoms. The lighting is really to blame too, I just have 2 300lm bulbs for 10-11 hours daily since I heard more light kills diatoms. I have come to think that removing 4 gallons (~25%) weekly is overkill, so I want to accumulate the nitrate in 1 month to 20 ppm, which is safe or 10-20 ppm. I saw on aqadvisor that 17-19% weekly water change is necessary, but my tests show otherwise. I feed my 9 bettas 2 strips of bloodworms in the morning, and 1 in the evening (I fed the same way with pellets). I threw out my pellets (regular aqueon pellets) because they had phosphates and they cause algae. I'm planning on getting an otto tomorrow to get rid of the algae. And buying 2 new 1400LM 15W leds.

amazon.com/gp/product/B00XU6LZGO

My question is, is this lighting sufficient or good, I don't want to spend too much on bulbs & electricity, I just want to steer clear from diatoms and keep my plants growing and alive. Also, can I just change my water once a month, if so, how much do I need to change to bring down 20ppm to 0 in an 18 gallon tank. Would this just make things worse because water accumulates phosphorus? Thanks everybody in advance!

Here are some pictures of my current setup:







 

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Sometimes water municipalities increase or decrease additives in the water, depending on what is needed for a particular area. As you already know, phosphates will increase the risk of diatoms in your tank. Check the tap water for phosphates. If it reads 5 ppm or above you may need to add a phosphate reducer to your tanks filter. Keep in mind that playing with phosphate levels can sometimes cause other types of algae... it's tricky to get it just right.

We use the Salifert Phosphate Test Kit. It's really easy to use and is quite accurate.
 

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More light will not kill diatoms, that makes them worse. Cut back to 7-8 hours a day with an hour or two of darkness in the middle of the day.
 

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Discussion Starter · #4 ·
Well, I heard elsewhere that brown diatoms do bad in high lighting that's why I increased it. I did wipe the glass, plants and decorations out of the tank and now I can see less diatoms spreading after a week. Also, about the water changes... I had previously changed 4/16 gallons weekly. But now I want to change it to every other week or once month since nitrates are always at 5-10 ppm weekly. Tomorrow I'm going to change the water and it's likely going to be at 10-20 ppm for nitrates. How much water do I need to change in order to bring down nitrates? I have 8 bettas in the tank and I feed them 2 pellets in the morning and 1 in the evening.

My normal weeky readings before water changes are:

Ammonia: 0
Nitrites: 0
Nitrates: 5-10 ppm
PH: 7.6-7.8
Temperature: ~80
 
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