Plant Growth Question

I must know the answer to this question:

Why is it that when I do a water change (40%), my plants grow straight up for the next 2 days? After that, they will grow more laterally, or will bend a little. I've witnessed this for the last 2-3 months now. This is most apparent in my H. zosterifolia & R. rotundifolia. It affects all plants, but the other's aren't so drastic.

I change water every 4-5 days. All nutrients are good; I'm following the EI method. Pretty much everything is constant, including insane plant growth.

 

Re: Plant Growth Question

It makes me wonder about those "ultra trace" nutrients...

Here are my water/dosing/equipment specs. I do not test anymore:

75g
Eheim 2028
Marineland HOT for extra mechanical filtration & water circulation
4x54w T-5 @ 6500K
Onyx sand top layer, Flourite bottom layer
Pressurized CO2 @ 30ppm+
40% wc every 4-5 days
KH = 13; GH = 18 (roughly)
1/2 rounded tsp. KNO3 EOD
1/8 tsp PO5 EOD (maybe a little more)
15-20 mL Flourish EOD
10-15 mL Flourish Iron once or twice a week

Water circulation isn't where I'd like it to be, but it's not bad. My impeller on my Hagen 802 powerhead broke and I have a new one coming later this week. That thing can move some water!

There's very little algae, just some tiny hairs on a few leaves; I suspect it would be nonexistent if I had a bunch of shrimp. This tank has reached that "balanced" stage where you can just dump in nutrients and the plants only grow faster. Judging from the plants, and I never thought I'd say this, but TB's dosing recommendations are actually lean!

While I'm at it, for my particular tank, does KNO3 supply enough potassium? I don't see any holes in any leaves, so I'm thinking yes? The tank is super-densely planted with many fast growers.

Thanks!