Really High Phosphates And Slow Growing Plants

[Kissaragi]

I have a 100L planted tank thats been showing really high phosphates for about a month now. P levels were at 0ppm before i started using NPK fertilizers, and then managed to hold them at 2ppm for a couple of weeks. All of a sudden they leapt up to 5ppm+ (my test kit only goes to 5ppm and the tube goes really dark blue in about 20 secs), I obviously stopped adding P but carried on with trace, N and K and weekly 50% water changes but im still 5ppm+. Im even using ROWAphos in my filter and it hasnt had any effect.

My plants have also been growing very slowly for the past 3 months, i had great growth for the first 6 months then they just slowed to a crawl and havent picked up since.

I do know the tank is over stocked as i have three small goldfish in there, but im going to rehome them this spring.

Tank specs are:
100L
65W lighting
Pressurized Co2 at 30ppm
Ph 6.8
Nirates held at around 15ppm
Temp (its an unheated tank) 23c on average

 

[Themuleous]

Are you getting algae? If not then dont worry about the P reading. Could the high P be a dodgy test kit?

What plants do you have and what substrate.

Sam

 

[Kissaragi]

The phos test kit does show a different result if i test tap water (2ppm). Worth taking some aquarium water to my lfs to check it do you think?

Im getting a small amount of green spot algae on the glass, and i think its hair algae the anubias leaves, Much less than before i put the co2 in tho.

I have some java ferns, quite a bit of Giant Hygrophila, couple of anubias nana(which are being eaten by the apple snails as i type), one anubias barteri, one echinodorus osris and what i think is Egeria densa. Also some bog wood and stones.

The substrate is small aquarium gravel with laterite mixed in the bottom.

 

[Kissaragi]

Im going to be taking this tank down and starting a new 250L in the spring anyway, but i just want to know what im doing wrong so i dont make the same mistakes again.

 

[Themuleous]

Sounds like a lack of plants to me, with that much light over a 100lt you need lots of plants, 75% of the substrate covered. I take it you're doing EI?

Sam

 

[Kissaragi]

Ye EI minus the P04 atm.

Its about 50% covered. I did buy a couple of crypts that i thought would fill out nicely but the snails ate them down to nothing. Also tried java moss but the goldfish ate that. Could excess Phos cause the plants to grow slower?

 

[Themuleous]

I wouldnt think so

Sam